Iran is pretty fucking transparent with their goal: to destroy the Zionist entity. The posters literally say "wiping Israel off the face of the Earth is just the beginning". And no, they don't mean "dismantle the state mechanism" like some users here claim. They very much mean it in the "death to the Jews" way.
Framing it as purely defensive is just lying
In all honesty, there are a few outcomes that are potentially worse if he is dead: Hamas splintering into many smaller factions, or treating him as a silent leader and refusing to release hostages because "he hasn't ordered it".
Hopefully Hamas will confirm and whoever replaces him will agree to release the hostages.