She doesn't stay dead, for what's it's worth. She had vampire blood in her system, not that I knew it at the time. [She doesn't mention the Elena here is the vampire version now.
It isn't her secret to tell.]
But all things considered, Matt's friends have their reasons for not liking the idea, he has every right to be unsure. I've tried to make things right but there are things you can't truly apologize for. Things you can't simply undo just because you wish to.