theres no way sylvanas can stay warchief simply because everyone keeps saying theres no peace while she's warchief.
we all know blizzard will try to redeem her. the standard way to redeem a character as evil as sylvanas is to have her die as part of the redemption. just like darth vader. that way you avoid all the awkward questions that come after the redemption like the alliance asking uhhh what about all those night elves you killed
however blizzard don't understand the fundamentals of storytelling. last time they tried to redeem an irredeemably evil character was in warlords of draenor with grom "i fuel my portals with home-grown draenei kids" hellscream. even though the narrative structure of the game demanded his death they went with "draenor is free!!!" instead. and we all know how that turned out.
they could easily do it again and try to have sylvanas be redeemed and live which would be such a ridiculous decision that i kind of hope they do it just to see how stupid the story of this garbage expansion can possibly get.