I don't know... the way this part of the actual story ended was with Bolas using an army of mind-controlled dragons (with Yasova's help) to strike Ugin out of the sky. Bolas then figured that Ugin was dead (or close enough that he had no way to recover) and left Tarkir thinking he had done what he set out to do; but then Sarkhan happened to be in the right place at the right time with the right tool to create
a protective cocoon around Ugin, keeping the Spirit Dragon from bleeding to death (or whatever) and allowing him to recuperate until awoken a thousand years later.
Sarkhan's win-condition ability was designed to replicate this; the idea being that if Bolas thinks Ugin is dead and leaves the plane, but Ugin isn't really dead, that's a win for Ugin. I guess for it to really work, though, Bolas would have to actually believe that Ugin is dead, and after hearing the discussion on the thread here today, that would certainly not be the case. Nicol Bolas is a smart guy (that's an understatement; he's been around for at least 23000 years and is ridiculously intelligent). If he caught wind of Sarkhan's shenanigans in the actual story, he would've done everything in his power to either kill Sarkhan before the cocoon could be completed or destroy the cocoon after the fact.
I guess to capture this more accurately in a game of Werewolf, Sarkhan's ability would only trigger if Bolas somehow orchestrated Ugin's death... I guess, by wolfkilling him, having a converted Acid-Spewer or Lightning Shrieker target him, or by having a majority of the converted lynch votes be on Ugin.
I have been considering running this game again sometime with only a few changes. I'm writing them down at the bottom of the rolesheet as I write this.