run flats

I just bought my first BMW in June. I found a cherry 2007 335i convertible with most of the bells and whistles. i was driving home form Chicago the other night and one of my rear run flats blew. I couldn't make it all the way home. Roadside assist. took it to the local dealership. they are telling me that both rear tires need to be replaced at $400= a clip. i started looking on the internet and realized that some of the ride issues on my car are because of the run flats. i'm wondering if I should replace with conventional tires for cost and ride? the biggest issue is of course breaking down on the road. i'm sure this is a common issue but being new I need some wisdom.