You should worry more when they stop arguing. My marriage broke up because my x-husband could not stand any form of confrontation. Any relationship that is a good one; will have confrontation at some point or another. It is about communicating.
I think your parents actually have a healthy relationship by the sounds of it. Hang in there, I bet hey work it out.
I agree with Oriani: keep your distance! It's a nature of marriage. And divorce is not the end of the world: I based on my own experience, I'm divorced. And believe me, we are better parents than couple. :)
Divorce is the best solution. If my parents had managed it, my mother's blood pressure wouldn't be so high now cause of my father! I mean she would be more healthy!
:( This is really a sad situation. But even brothers and sisters do argue, so I think, there's no way to stop them. But they will eventually reach a compromise.