Monster Life reactions

Today's dumb question: what happens if you don't nurture your monsters when they get those hearts over their heads?

Can they de-level? Die? Run away? Any other ill effects?
Also, the game tells me I'd get more experience by nurturing monsters that want it - but I don't. Nurturing gives 10 exp regardless.

I think it ment to tell you that your monster (not you) gets more experience when it wants nurtured and you nurture it.
(Monster exp = gain levels for the monster, your exp = get a higher level farm.)