During JK's reading, the question was asked which characters she would have over for dinner if she could. She replied "Harry, to apologize" and then "Ron and Hermione". At this point people started shouting out characters and she said "But I know who dies". Then, as if realizing this implies the ones she'd already mentioned live, she added Dumbledore and Hagrid.
Now, there is also the fact that Emerson from Mugglenet said that back before HP became famous, JK was asked by a kid if the trio survive the series– and she said yes. Of course, she did say recently she killed off two she didn't expect to– but she mentioned it as if the two deaths had caused slight alterations to the epilogue. I think any of the trio dying would cause at least a few chapter's rewrites, don't you?
In conclusion, it has always been my belief that the trio will live. And, by golly, now here's a bit of evidence to make that case. (Ignore the fact that I said "by golly" and try to think more OMG! TRIO LIVING!)