I'm sure it depends on every single case. I've dated several close friends, and they ended for a variety of reasons, but beyond a short duration of awkwardness and/or bitterness, I've been able to maintain all of those friendships. Took a little work sometimes, but in the long run, I don't regret giving any of those relationships a chance. Besides, we understood the stereotypical risks of those dating-friends scenarios going in, so there was a common understanding.
Still though, I'm sure some of that depends on why such a relationship would end. If one person really hurts the other, yeah, maybe that wouldn't allow for any continued friendship.
Anywho, long story short, I don't think you should actively avoid getting involved with a friend. It might be something the two of you discuss somewhat beforehand though, although probably not too much as over-analyzing anything isn't going to be good, or you'd just end up protecting yourself too much. For me, I need to be pretty close to someone to consider it. I'm not particularly into the whole dating scene, and just meeting people and jumping into a romantic relationship. Doesn't really work for me.