Is it disrespectful to leave after the service and not stay for the burial?

I don't think it's disrespectful at all. I don't even go to funerals. I give the wife or family a call and tell them how sorry I am, how sad it is, what a great person he or she was, and that he or she will be remembered, and I let it go at that. Funerals are for the living, and as far as I am concerned they are entirely gratuitous (meaning, in this case, -optional-).