What Will Happen If I Ate Something That A Mouse Ate On And I Didn't Notice It?

I do not think you will die. Last year I
discovered that a mouse had nibbled
on my chocolate rabbit. I still ate it
because it cost me five bucks, and
I'm fine! Mice can carry disease, fleas, etc.
But I would only be worried if you had rat/mouse
poison lying around that the mouse could have
eaten, or if you had consumed its feces
or urine (but even then, parasites are rare).
Your immune system should fight off anything.
I would of course advise you to cut off the section
of food with bite marks on it if you ever come across
edible victims of rodent nibbling. A dog or cat
licking your food would be much worse than a mouse;
at least mice don't lick their a****!