I see no reason at all to throw them out. As Trevor mentioned, I've soemtimes left prey overnight, and if refused, re-frozen it, but never more than once. After that, if I don't have a serpent garbage disposal unit available to take the prey, it goes in the garbage.
Snakes deal with bacteria ALL THE TIME. Keep in mind that whatever prey you feed them is going to develop and release bacteria as it is digesting anyway. Is the rodent's body not decomposing in the snake's stomach? If so, and it is releasing bacteria, how is that any different than if it ENTERS the snakes stomach with some decomp bacteria? It isn't. Bacteria cannot survive an environment as hostile as a snake's stomach. If it does, it cannot do any harm, or it would do that harm every single time your snake ate.
- Ken LePage