Personally I think (warning: I know essentially nothing about GoT and ASOIAF except what I've read after finding this mod so my opinion can probably be easily invalidated) that the Valyrian religion as it was would probably have been more or less died out with Old Valyria in the Doom. The only way we could see a major resurgence of the Valyrian faith is if Aegon decides to continue following it instead of converting to the Faith of the Seven (Westeros) or R'hllor (Essos/New Valyria) and attempts to convert his conquest. Remaining a follower of the Valyrian religion, or even conquering the Free Cities instead of Westeros, seems like it'd be a non-cannon choice, so like I said earlier, maybe it could be used as a "what if" scenario where, after completing his conquest and refusing to convert, he could "reform" or "revive" the Valyrian faith into a more mixed religion with certain aspects of both Valyrian and the local religion in an effort to make his new subjects more willing to convert? For instance, both mixed religions could gain the ability to have multiple wives, brother-sister marriages, and maybe some dragon-related ritual from the Valyrian religion if you wanted to be creative. The Seven/Valyrian religion could try to use a system similar to the High Septon with the Oldtown holy site replaced by the Dragonstone one, knighthood and tournaments, and the faith authority mechanic from the Faith of the Seven, but potentially have fewer qualms against slavery in exchange for greatly alienating followers of the Old Gods. The R'hllor/Valyrian mix would probably have a religious structure based off the R'hllor faith, perhaps claim that dragons are servants of R'hllor himself, impliment the Favored/Chosen by R'hllor but have a special requirement that a character needs to be a dragon rider or something similar, and potentially be more likely to trigger a slave revolt due to the slaves viewing it as the return of a tyrannical empire that will enslave all of Essos if it isn't stopped.
Honestly though, I think I'd be content with the current Valyrian faith being able to build temple structures and take advantage of the Seven's knighthood and tournaments if in Westeros.