It would be very unlike Ars Magica to confirm or disconfirm any such thing. Much better to preserve the mystery, so that magi can debate it authentically in character, and each troupe can tell their own story, with no plot spoiled.
This is what I really love about Ars Magica.
Both human sacrifice and diabolism have been put forth as the principal allegation over the editions. Its being the largest and military strongest house is probably close an important reason. Some sources AFAIR present them as bullies. Pagan and non-Latin caused some distrust too, but so are Bjornar, so that is probably second to other reasons.
There were underlying tensions of course, but the immediate trigger for the war was probably suspicions of diabolism (this was shortly after the Tytalus diabolism scandal, so suspicions were widespread) together with the fact the House Diedne refused to let Quaesitors in to their covenants to investigate these accusations.
The accusations of human sacrifice may have been true (House Tremere certainly believe so) , but that by itself was not a violation of hermetic law.
In the end it was largely a choice between letting the whole Order dissolve into chaos and violence, or direct all that violence onto a single enemy - House Diedne.
Tremere will lose face, which given their current efforts they will attempt to recover by offering more assistance to others, and might even use that as a reason "we are trying to improve our reputation after the Diedne debacle" to cover their real intention of "we are trying to get you dependent on our infrastructure and organizational ability".
The biggest shift is that the Diedne magic flaw stops being a flaw and becomes a virtue for the spontaneous magic abilities they have.
It really depends on what you want to happen in your saga. I recall in a game I only heard of via, the web, they found information like this along with the Tremere being Vampires, in a 4e game set in the late 90s. The saga followed a very long political Arc where the PC's founded the OoH equivalent of NATO, marched the vampiric Tremere and forced the non vampiric members into other houses and disbanded the house.
Then had a shorter follow up saga on, well, what do we do now? @Tuura or @Kryslin actually participated in the game and could explain it better. I was only 14 when they told me about it (closer to 25 years ago than I would like) and I read some of what they posted on an old Ars Magica forum.
I just had this image of a world where the Criamon cycles of time were fundamentally true, in which this was the fifth world, with the 3rd world having collapsed during the World of Darkness and prophecies survive amongst certain mystics with warnings to prevent such a fate from ever happening again (each edition being a previous cycle of time)
Even if no travel is possible and nothing survives, the mere possibility of visions of the future being actually visions of the past is quite nice.
I can even see some magi being worried about all these mystics that have visions about the Vampiric Tremere, tested and "proven" not to be an infernal subterfuge by any and all means possible (mentem magics, sense holiness, whatever), save that it absolutely doesn't apply to current Tremere, something which they have no way to know.
What if some Diedne Mage would come out and request to the Grand Tribunal to be made a house again ?
5 of them would create a covenant and get aprentices but some hateful mages would just wipe them of (knowing they would get hunted down afterward).
The 5 aprentices would be protected by one house and allowed to create their own coveneant.
(And yes, that is the campaign i'm starting atm with some friends).
We now have 5 young Diedne mages with the mission to recreate their house but very few knowledge on how to do it and a lot of eyes watching them closely for the tyniest mistake...
So the older Diedne were wiped out but their apprentices were left alone and don't feel like they need to go into hiding for their own safety? That seems like a heck of a stretch to me.
Sub Rosa 13 has a bunch of interesting material for Diedne. If you are going to play a game in which the House is found innocent, it has several ideas on how bits and pieces of the House might have survived.
I also ways had the impression that the Diedne was innocent and that it was a power play by the Tremere and the Quaesitor and Tyalus join in for the conflict or was tricked to helped
Technically that's up to the GM to decide but we though in my group that it would make an original campagin...
Now we have some youngsters protected by House Guernicus and we'ell se how they plan to revive their own traditions
Think about it this way:
You run the game once, with the Diedne as the good guys that were framed, and it opens up conflicts within the Order because then the Flambeau, Tytalus, and Guernicus have used the code against an entire innocent House. There are consequences for this. what they are depend on your players, and the inter-house dynamics in your game.
You end the saga, and your players encourage you to run another saga, but this time, you decide to have the Diedne be guilty. If the players investigate it, sure that the proof will be the same as previous saga, they are in for a surprise. it's like an entirely new saga, and who knows what other secrets uncovered in the previous saga remain the same...
I have played in / played in campaigns where it did not matter to the campaign. One it never came up and one where the players ignored anything to do with the Diedne. In my current campaign that has been going on for over 8 years, Diedne is not an issue. Being in Iberian The group has more pressing matters than what happened in the past.
Of course. Diedne is supposed to be extinct, and should not surface often. My point was more that different stories should be told each time they do surface, and assigning them to different roles each time is part of that. Good stories can be told with Diedne as dirabolists, with Tremere as the big and dishonest bad concocting the story of diabolism, and with just a just human conflict that got out of hand. Telling the same story again is just boring.
I did try once When I ran the tempest that group did seem to care about the reason why the diene was doing the things to the covenant. Opening it up as a way to avoid frightening him. but it was not to be too many D&D players in that group. I would like to try a Diedne as maybe as a player character but the virtue for the Diedne that was in the Tempest was too powerful for a +1 Virtue. never got around to trying to rework it.