Zac's passive is just an effectively longer respawn timer....
Unless you kill your opponent with your cinderquill while on the ground there is very little chance of you getting revived. Almost every champion in the game can kill you before you repsawn, your blobs can be smited, they increased damage due to loss of resistances, and they have so little HP. I'd honestly rather they just remove the revive passive and put power somewhere else into his kit, maybe give us that ult tenacity back so we don't just nailed by a Morgana binding and lose our entire ultimate?