Not sure what you mean by what happens to them in the bin - They soak up water and remain plump with water until the bugs suck it all back out and it usually leaves behind a little crusty blob.
Yeah if you put more water on them once they dry up they will reabsorb. Mine are usually covered in cricket poo so I don't reuse them but I have considered cleaning them and reusing. I know they go back to original size from ones that have been left in the sink drain...