MZAFZ is not dead yet. In Minister for Immigration and Border Protection v CQZ15  FCAFC 194 at  the Full Court confirmed the possibility that an applicant might want to (and be entitled to) demand production of documents covered by an invalid s 438 certificate, because those documents might show denial of procedural fairness or apprehended bias.
If a denial of procedural fairness has deprived the applicant of a fair hearing, there is no need for the applicant to prove anything more. This is contrasted with the situation where a denial of procedural fairness did not otherwise result in a fair hearing (probably a rare situation).
See discussion in Minister for Immigration and Border Protection v WZARH  HCA 40; 256 CLR 326: per Gaegler and Gordon JJ at -:
The concern of procedural fairness, which here operates as a condition of the exercise of a statutory power, is with procedures rather than with outcomes. It follows that a failure on the part of an assessor or reviewer to give the opportunity to be heard which a reasonable assessor or reviewer ought fairly to give in the totality of the circumstances constitutes, without more, a denial of procedural fairness in breach of the implied condition which governs the exercise of the Minister’s statutory powers of consideration.
Such a breach of the implied condition which governs the exercise of the Minister’s statutory powers of consideration is material, so as to justify the grant of declaratory relief by a court of competent jurisdiction, if it operates to deprive the offshore entry person of “the possibility of a successful outcome”.
That approach to the determination of the existence and consequence of a breach of an implied condition of procedural fairness governing the exercise of a statutory power is wholly consistent with the often-repeated observation of Gleeson CJ in Re Minister for Immigration and Multicultural and Indigenous Affairs; Ex parte Lam that the concern of procedural fairness is to “avoid practical injustice”, and with his Honour’s conclusion in that case that there was no denial of procedural fairness where “[n]o practical injustice ha[d] been shown”. The absence of practical injustice in Lam lay in the fact that “[t]he applicant lost no opportunity to advance his case”; it was not “shown that he lost an opportunity to put any information or argument to the decision-maker, or otherwise suffered any detriment”.
Contrary to the submission of the Minister in this appeal, and as has repeatedly been recognised in the Full Court of the Federal Court, Lam is not authority for the proposition that it is incumbent on a person who seeks to establish denial of procedural fairness always to demonstrate what would have occurred if procedural fairness had been observed. What must be shown by a person seeking to establish a denial of procedural fairness will depend upon the precise defect alleged to have occurred in the decision-making process.
There are cases in which conduct on the part of an administrator in the course of a hearing can be demonstrated to have misled a person into refraining from taking up an opportunity to be heard that was available to that person in accordance with an applicable procedure which was otherwise fair. To demonstrate that the person would have taken some step if that conduct had not occurred is, in such a case, part of establishing that the person has in fact been denied a reasonable opportunity to be heard.
Where, however, the procedure adopted by an administrator can be shown itself to have failed to afford a fair opportunity to be heard, a denial of procedural fairness is established by nothing more than that failure, and the granting of curial relief is justified unless it can be shown that the failure did not deprive the person of the possibility of a successful outcome. The practical injustice in such a case lies in the denial of an opportunity which in fairness ought to have been given.
In Minister for Immigration and Multicultural and Indigenous Affairs v SCAR  FCAFC 126, the Court observed:
 On the other hand, it is also clear that s 425 of the Act imposes an objective requirement on the Tribunal. The statutory obligation upon the Tribunal to provide a “real and meaningful” invitation exists whether or not the Tribunal is aware of the actual circumstances which would defeat that obligation. Circumstances where it has been held that the obligations imposed by s 425 of the Act have been breached include circumstances where an invitation was given but the applicant was unable to attend because of ill health: Applicant NAHF of 2002 v Minister for Immigration and Multicultural and Indigenous Affairs  FCA 140. They also include circumstances where the statements made by the Tribunal prior to the hearing have misled the applicant as to the issues likely to arise before the Tribunal: VBAB of 2002 v Minister for Immigration and Multicultural and Indigenous Affairs  FCA 804. They also include circumstances where the fact or event resulting in unfairness was not realised by the Tribunal. For example, circumstances such as where the applicant was invited to attend and did attend before the Tribunal, but was effectively precluded from taking part because he could not speak English and a translator was not provided or was inadequate: Tobasi v Minister for Immigration and Multicultural Affairs  FCA 1050; W284 v Minister for Immigration and Multicultural Affairs  FCA 1788.
See also SZQBN v Minister for Immigration and Border Protection  FCA 686; 226 FCR 68 at  per Flick J and Gill v Minister for Immigration and Border Protection  FCAFC 51 at  per Griffiths and Moshinsky J.
The proposition is trite but sometimes overlooked.
A modern High Court migration authority for this proposition can be found in SZBEL v Minister for Immigration (2006) 228 CLR 152, .
In BMF16 v Minister for Immigration  FCA 1530, Bromberg J said at -:
222. In Ucar, following a comprehensive survey of the authorities, Redlich JA (with whom Warren CJ and Chernov JA relevantly agreed) stated (footnotes omitted):
In my view, the principle laid down in Stead contemplates two circumstances in which relief may be refused. It will be refused if upon analysis of the basis for the decision there is an incontrovertible fact or point of law which provides a discrete basis for the decision which cannot be affected by the procedural unfairness. It will then be concluded that the applicant could not possibly have obtained a different outcome. Second, even where the subject of the procedural unfairness touched upon an issue in dispute that was material to the decision, relief may be refused if the respondent can demonstrate that it would be futile to hold a further trial because the result would inevitably be the same.
223. As to the first circumstance contemplated by Stead and referred to by Redlich JA, there is no incontrovertible fact or point of law which provides a discrete basis for G’s refusal decision which is not affected by the procedural unfairness which I have found. As for the second circumstance contemplated in Stead, it was for the Minister to demonstrate that it would be futile to set aside G’s refusal decision because on a reconsideration, the result would inevitably be the same (as to that onus see also Hayne J in CSR Limited v Della Maddalena  HCA 1; (2006) 80 ALJR 458 at ).
224. In any event, and putting aside questions of onus, as McHugh J said in Re Refugee Review Tribunal; Ex Parte Aala  HCA 57; (2000) 204 CLR 82 at  (in a passage later referred to by the Full Court in VAAD v Minister for Immigration and Multicultural and Indigenous Affairs  FCAFC 117 at ), “once a breach of natural justice is proved, a court should refuse relief only when it is confident that the breach could not have affected the outcome”. Where the issue is whether additional evidence and submissions could have affected the outcome of the decision-maker’s consideration of the matter, it cannot normally be said with certainty that affording such an opportunity was futile: VAAD at  citing Kirby J in NAFF at . It will be “no easy task” (Stead at 145) to satisfy a court that a denial of natural justice could have had no bearing on the outcome.
The reference to Aala was most recently re-endorsed in Gill v Minister for Immigration and Border Protection  FCAFC 51.
The weight of authorities focus on how alleged misinterpretation may have distorted the overall process. For a discussion of recent authorities and application, see eg:
In the key case of SZRMQ v Minister for Immigration and Border Protection  FCAFC 142; (2013) 219 FCR 212, Flick J was in dissent as to the standard of interpretation required; the majority concluded that some margin of misinterpretation could be tolerated whereas Flick J appeared to conclude that the standard expected of an interpretation is higher.
Section 426 of the Migration Act requires the Tribunal to ‘have regard to’ an applicant’s request to obtain further evidence from, or call, a particular witness. The Tribunal is not required to in fact do so.
However, the authorities are clear that the question of whether the Tribunal should is a discretion that must (therefore) be exercised reasonably.
In addition, the Tribunal cannot ‘merely go through the motions’–there must be a genuine consideration of whether to exercise the discretion: CBZH v Minister for Immigration and Border Protection  FCA 1023.
Also, in BOL15 v Minister for Immigration and Border Protection  FCCA 1994, Lucev J said:
Whether or not calling the Applicant’s Proposed Witness may have resulted in evidence being given which did not assist the applicant is not to the point, rather, the Court cannot preclude the possibility that such evidence might have assisted the applicant to establish his claims
At  of SZSSJ v Minister for Immigration and Border Protection  FCAFC 125 the Court recited the basic principle:
The Federal Court concluded in Minister for Immigration and Citizenship v SZQRB  FCAFC 33; (2013) 210 FCR 505 (‘SZQRB’) at 544-546  and 546  that the power of removal in s 198 could not be exercised whilst a person in detention had made claims for protection (including by way of non-refoulement) until those claims had been assessed by a process which accorded an applicant procedural fairness and which addressed the correct questions according to Australian law.
This principle arises from Plaintiff M61/2010E v Commonwealth  HCA 41; (2010) 243 CLR 319. The assessment of non-refoulement claims is the second step of the two-step process of the Minister deciding (step one) whether to exercise certain non-compellable powers (step two) such as lifting the bar (s 48A) or granting a visa (s 195A). Procedural fairness is required in the exercise of step two: M61.
The consequence is that detention of a person who has made non-refoulement claims, but such claims are not being considered, or being considered without procedural fairness, may be unlawful: see SZSSJ .