Feel like thats a broom and dustpan situation, both due to likely quantity of ash, and wanting to preserve them with minimal contamination for a urn or just ash spreading disposal.
Actually ordinary household vacuums are notoriously bad at sucking ashes from human remains. There are special vacuums for fireplaces and such that do way better job, Id recommend one of these
If The Sims has taught me anything it's that you should A) Freak out, B) Cry over the tombstone that suddenly appeared out of nowhere, C) Flirt with the personification of death that appears to reap the soul of your guest, D) Rate the party as a real downer and belittle the person throwing the party.
Bonus points for wetting yourself at some point during the whole ordeal.
Look, I invited him in and we had a wonderful time until dawn. Is it my fault the blackout curtains weren't closed all the way? Yes. Will Dracula be pissed? Only if he can regenerate from being disintegrated. The relationship was just getting a little too claustrophobic for my liking.
freak out and talk about it with people before it potentially happens to me too and maybe start a livestream so if it does happen it'll happen on live even though nobody will probably believe it