My opinion only here, but expect a portion of the players to drop. Some always do. Gathering a list of potential sitters could be valuable at some point. Role-Play is awesome, and encouraging it is all you can really hope to do.
-yc
I expect drops. I'm just doing my best to discourage them.
Gathering a cadre of sitters though is likely a good plan, although always hard to pull off until you're in the moment and know what a person's present commitments are.