That sucks, man.
One of ours died at the vet's office a few years ago. She developed an intestinal block and we didn't notice it until it was too late. They had her for three days - first night we thought she was done for and braced ourselves, but the second night she seemed better and we thought she'd pull through. The phone rang at 9:00 the next morning.
And, of course, the dead cat came with a $600 vet bill. Hopefully you were at least sparred that indignity.
And I concur with being very leery of the shit they're paid to peddle. Our old vet pushed Science Diet pet food, for example, which is both shitty and overpriced. We don't use them anymore.