I believe the Tevinters come later in the game if you take certain decisions.
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Maybe. I theorised that, since Tevinter is not particularly in a good term with its neighbours, they probably rejoiced to learn that the mages rebelled to get their freedom. So, I think that Tevinter possibly tried very soon to participate and support this revolt, either directly or more discreetly.
Also, all the mages that revolted or fled the circles should be called "apostate". And since they don't share a hive mind, I'm expecting to witness some dissension between them. Soooo I think that it's possible that a (small?) part of them have accepted the help of Tevinter ( if Tevinter proposed its help in the first place, of course). And that they organized themselves around this Tevinter guy in Redcliff.