My question started after looking at the nominations right now and seeing a very strange nominated user who appears on other sites for nomination and has little score in all. This makes me wonder a lot about the intent to go for moderator and what could happen.
People want to become moderators for a great variety of reasons. Some high rep users make terrible moderators, and some low rep users turn out to be excellent. I suggest not jumping to conclusions. :)
Participation on the site is likely an indicator of how invested the person is, but it's not always a good measure of how they would perform as a moderator. No amount of reputation, badges, etc. is going to guarantee that someone will be good at moderating.
With all that said, almost every action a moderator can take is reversible. If a moderator were to go full on rogue, we can recover fairly easily. What you will usually see is an occasional mistake that's easily solved via meta or a review by another moderator.
If all else fails, though, we have a process for removing an unfit moderator, but it rarely comes to that.
And last but not least, every moderator is bound by an agreementan agreement. Violations of that agreement will result in a speedy diamondectomy.