Can a bent mt bike rim be repaired.... it is still ridable?

A bent rim being repairable wholly depends on how it's bent and how bad it is. If is slightly out of true it usually an be trued to near perfect. If it moderately out of true it can be trued good enough for most riders. If it's bad, badly dented or kinked it likely needs replacing. Only the person doing the truing will know for sure.

If it is a steel rim from a low-end store mt bike, then it probably isn't worth the effort. You can replace the wheel pretty cheaply if you find the right bike shop.

HTH

That's something I wouldn't mess with. If the rim is bent, replace it. You could start ripping the side walls of tires.

Hard to say. If the rim is DENTED, like if your tire was underinflated then no, it cannot be repaired... trying to bend it back will result in the rim cracking.

If it is "wobbly" or out of true then chances are it CAN be fixed. There are some conditions in which it can't, but only a shop can determine that.