I spy a question:Do you think if Carlise had the chance to become human again that he would take it?
I don't think so. Maybe he would have before, but now he's found a wife and a 'famil', he can't and wouldn't want to leave them. He has a job where he saves lives, he's got perfect self-control, and he's used to being a vampire.
Also, being a vamp and having all the extra strength and speed is kind of cool.