I wouldn't say there is never a chance. If my ex girlfriend re-appeared I would definitely go there.
But-I broke her heart, so she isn't going to. Friends she will allow, but more than that-no way.
The thing is, that there are situations I could see it happening in. But they are rare.
If whatever caused the breakup is resolved, no reason not to try again.
"Love As Thou Wilt"