I noticed that Twitch's passive stacks would disappear from Aatrox when Aatrox's passive was triggered. I feel that the stacks should stay. Aatrox could still be invulnerable but the stacks could stay. That way, I don't have to completely restack my passive just to any type of significant damage to him with Expunge.
Aatrox passive removes any debuff. Pretty sure Zilean ult and Zac passive works the same way. I also don't see it usually being a problem as long as you used E to get him to start resurrecting.
the reason why aatrox, zac, zilean, anvia, or any champ with 
on drop all debuffs is because they all technically "die" before their respective rebirths through passive or item and as we all know when you die all debuffs and whatnot are removed from the champion. so when they revive they obviously wont have say stacks of bleeding or twitches passive or even say 
' passive
