Regarding Gregory of Nyssa
(GoN) as witness for 16:8 original it would appear that the Apologist John Burgon
(JB) is the source for modern Apologists' not mentioning Gregory. Burgon's god-awful The Last Twelve Verses of the Gospel According to S. Mark Vindicated Against Recent Critical Objectors and Established
is freely available and well worth the price of omissions (from this site you can likewise freely download the E-book and what a load it is!)
On page 39 JB confesses that GoN is credited in general by Christian Bible Scholarship (CBS) with writing that supports 16:8 as original:
Gregory of Nyssa. This illustrious Father is represented as expressing himself as follows in his second " Homily on the Resurrection 0 ;" — " In the more accurate copies, the Gospel according to Mark has its end at ' for they were afraid.' In some copies, how ever, this also is added, — ' Now when He was risen early the first day of the week, He appeared first to Mary Magdalene, out of whom He had cast seven devils. ...[Greek] Opp. (ed. 1638) iii. 411 B.
JB then claims on page 40 that Hesychius wrote the same thing so you can only count one of them as a witness:
word for word the same Homily which Combefis in his " Novum Auctarium," and Gallandius in his "Bibliotheca Patrum" printed as the work of Hesychius,  and vindicated to that Father, respectively in 1648 and 1776*.
per Ben Smith's great site though this is the related Hesychius evidence:
From Hesychius, Collection of Difficulties and Solutions, question 52 (century V):
Διαφορως γαρ προς το μνημα δραμουσαις, ου ταις αυταις γυναιξιν, αλλα ποτε μεν δυσιν εξ αυτων, ποτε δε μια ετερα παρ αυτας τυγχανουση, ποτε δε αλλαις, διαφορως και ο κυριος εφανη, ων τη μεν ως ασθενεστερα, τη δε ως τελειοτερα τυγχανουση· καταλληλως εμετρει τον εαυτου εμφανισμον ο κυριος. οθεν Μαρκος μεν εν επιτομω τα μεχρι του ενος αγγελου διελθων, τον λογον κατεπαυσεν.
For [he appeared] to different women who had run to the tomb, not to the same women, but now to two from among them, and then to the other one who happened to be with them, and then to others, and differently did the Lord appear, to one of which who was weaker, and to another who happened to be more perfect. The Lord measured out his own appearance appropriately. Whence Mark, having gone through in brief the things until the one angel, ceased the word.
Hesychius takes a somewhat different approach to the ending of Mark than does Eusebius. He neither tallies manuscripts nor opines as to which are the more accurate; rather, he simply takes it for granted that the text of Mark ends at the single angel, by which I presume he means the young man of 16.5-7. For Hesychius this ending is something that calls for explanation, but it is his best judgment nonetheless.
This is completely different evidence from Hesychius. Either JB was unaware of it or he is being dishonest.
JB is not finished trying to use the supposedly same Homily to minimize witness to 16:8. Still on page 40 he than attributes the same Homily evidence to Severus:
(2.) Again. Inasmuch as page after page of the same Homily is observed to reappear, word for word, under the name of "Severus of Antioch," and to be unsuspiciously printed as his by Montfaucon in his " Bibliotheca Coisli- niana" (1715), and by Cramer in his "Catena8" (1844),— although it may very reasonably become a question among critics whether Hesychius of Jerusalem or Severus of Ant was the actual author of the Homily in question
Here Severus' evidence for 16:8 looks just like Gregory's:
Severus of Antioch.
From Severus of Antioch, homily 77 (century VI):
Εν μεν ουν τοις ακριβεστεροις αντιγραφοις το κατα Μαρκον ευαγγελιον μεχρι του· Εφοβουντο γαρ, εχει το τελος. εν δε τισι προσκειται και ταυτα· Αναστας δε πρωι πρωτη σαββατου εφανη πρωτον Μαρια τη Μαγδαληνη αφ ης εκβεβληκει επτα δαιμονια.
In the more accurate copies, therefore, the gospel according to Mark has the end until the [statement]: For they were afraid. But in some these things too stand in addition: And having arisen early on the first day of the week he appeared first to Mary Magdalene, from whom he had cast out seven demons.
Severus, who also seems to have read Eusebius, agrees with Eusebius, and against Victor, on which copies are the more accurate. Severus does not explicitly tally the manuscripts, but that he mentions some (τισι) that contain Mark 16.9-20 may imply that most still lack it.
JB concludes as follows on page 41 that Hesychius is the likely author and therefore Gregory and Severus should be exorcised as witnesses:
(3.) In short, here are three claimants for the authorship of one and the same Homily. To whichever of the three we assign it, — (and competent judges have declared that there are sufficient reasons for giving it to Hesychius rather than to Severus, — while no one is found to suppose that Gregory of Nyssa was its author,) — who will not admit that no further mention must be made of the other two ? (4.) Let it be clearly understood, therefore, that henceforth the name of "Gregory of Nyssa" must be banished from this discussion. So must the name of " Severus of Antioch." The memorable passage which begins, — "In the more ac curate copies, the Gospel according to Mark has its end at 'for they were afraid,'" — is found in a homily which was probably written by 2 Presbyter of Jerusalem, — a writer of the vi* century.
We have the following reasons to think that JB is full of holy shpirit here:
The New Porphyry
- 1) CBS generally accepts that there are three here, Gregory, Hesychius and Severus, who witness 16:8 as original.
2) Even if a prior Patristic was copied exactly the default is that the subsequent Patristic agreed with the earlier Patristic.
3) JB's claim that "no one is found to suppose that Gregory of Nyssa was its author" is strange/bizarre/macabre given that he previously bitshoped and memed that current scholarship carelessly assigned it to Gregory.
4) Since JB has no reason then, not even a bad one, to assign the supposedly same Homily to a later author in a question of authorship, the default is the earlier one.
5) As pointed out Hesychius has other evidence against 16:8.