Sorry you are going through all this, rechu. Everyone else has really made some good points, so I don't have much to add.

I would say, if you think you might regret it later, after your mom passes away, you might want to pay a short visit (at SOME point before she passes away). More just for your own peace than theirs... but not visiting seems perfectly reasonable to me also. If and when you do visit, can you stay in a hotel and just see your parents for short periods of time?