Ah, the glory of headcanon, or “continuity wrangling” as we used to call it in the old days, a game that has only been made more fun by the existence of various expanded universe versions of Doctor Who. You got the TV series itself, the novels, the comic and the audios to play with.
So, the Big Finish canon and the Time War.
As far as I'm concerned (I know the point is considered debatable by some) the Rassilon in The End Of Time is the Rassilon. The Time Lords dragged him out of the Divergent Universe by means unknown and somewhere in the deep shadows of those council scenes in The End Of Time is lurking that “complete fraud and malicious piece of excrement” the Kro'Ka.
As to the Divergents themselves (who would have been resurrected in the new cycle started in The Next Life) I suppose that Rassilon probably used them as cannon fodder against the Daleks. Not in any particularly tactical way, just opened a portal from their universe in front of the biggest Dalek army he could find and watched the two slaughter each other, probably whilst eating popcorn (Big Finish Rassilon? Not a nice guy. Kind of a genocidal maniac, actually).
I think Romana's dead. I don't believe bringing Rassilon back from the Divergent Universe is something she'd have signed off on, I think the High Council did it after she died. If she died then Leela died too, probably protecting Romana.
Part of me wants to speculate on what Braxiatel did during the Time War but that would mean making some kind of sense out of Braxiatel's Big Finish timeline and that way madness lies. I think the version of Braxiatel from the Gallifrey series is the same Braxiatel from the Legion-era Bernice Summerfield box sets and the Braxiatel from the Collection-era is an alternate version originating in the New Adventures timeline. I am almost completely certain they're meant to be separate people and not the same guy at different points in his timeline. Maybe. Who knows? Not even Brax, as far as I can tell, so I've got no hope.
Contrary to what is going round the internet right now I don't think Big Finish will be doing the Time War ever. Its a very definite ending to their side of the continuity and endings aren't really something Big Finish are in to.
Oh, and the Visionary is the Pythia resurrected from the ancient Gallifrey of The New Adventures.