Your crew will quickly dipose of the carcass and the shell will most likely become a new house for a hermit when he decides to upgrade from apt to townhome. I leave all of my expired snails and hermits in the tank and they are quickly diposed of. Plus I think it looks cool when the floor of the tank is littered with different size and pattern shells, much like the ocean would be. Its really your choice.
I would watch your amonia levels, those things can be nasty if dead. I have taken all my dead ones out. By the way they smell really bad too, you might start smelling it, if your hermits don't eat it quickly.
Well I guess it depends on tank size, in a 10 gallon I would worry but since I have a 37 and a 75 one snail doesnt cause any problems and the hermits are pretty quick. Never had any bad smell or ammo problems, really depends on tank size.