That is along the lines of what I was thinking. I have a hard time believing some lizards could wipe out the most powerful Telvanni.... they are thousand year old wizards who can fly, teleport, and summon small armies of deadra. I would imagine with that skill set escaping would be an easy trick.
I ask these because my character is an ex-Telvanni wizard. Exiled because the temple and Empire found some of his experiments to be to far even for a Telvanni.
The Telvanni were not so much a house united on all fronts like house Redoran (remember Redoran, never forget)
as they were more akin to ancient Greece, more or less independant city-states.
Certainly every mage-lord ruled his demesne as he saw fit, and the covenants of house Telvanni practically encourage usurpation.
They state that if a Telvanni can get away with stealing from a Telvanni, he deserves his loot, and if he managed to kill another Telvanni mage-lord he is clearly the superior and deserves his holdings.
Right through might.
This attitude naturally led to individualism among the mage-lords and their personalities and interests were far more diverse than that of a more united house, such as the trading and politicking Hlaalu.
I have no doubt that some of the more excentric mage-lords like Dratha or Therana will have fallen.
Someone like Aryon might have perished defending the people of Tel Vos that he loved.
But someone like Demnevanni or Fyr?
They would have survived.
There must be reclusive, powerful mage-lords out there, especially on the mainlands, who would have continued their own projects and simply didnt care about the Argonian invasion.
Buried their tower or otherwise made it unseeable or inaccessible.
The city-state nature of the house, where each mage-lord more or less rules its own kingdom, would have contributed to the demise of the house proper, the fall of Telvannis, but at the same time would have ensured that at least some mage-lords came out of the war relatively unscathed.
As I said, I think some of the more private ones probably wont even have noticed the house is no more.