Answer 1:
Like most electrical mechanical devices, electric motors have mechanical bearings that eventually wear out.
The graphite brushes and commutator of older DC motors can also wear out over time
Answer2:
Question two is not specific enough!!
Are we talking DC?? Because if so, then yes, nothing will happen. Assuming you are insulted by ground.
Ac is a different story, as the two would light up dangerously and etc.
-your welcome!!