Other than going with your instincts (which can be really tough when you're stuck in the middle of the situation), the only thing I can offer is this: When it's all over, will you regret not trying one last option, one more treatment, one more medication? Will you beat yourself up over it if you don't try everything? Or do you know in your heart that it's only a matter of time and you don't want his last weeks to be miserable?
It's usually pretty easy to tell when they have had enough and it's time to let go. It's much, much harder to know when to stop treatments and move into a hospice-type level of care. Do you know your vet well enough to believe that she is telling you what you need to hear and not what you want to hear?
Mom to Roxi (fawn, 05/2000-06/2012), Harley (white, 03/2006),
and Turbo (fawn, adopted from AABR 12/2008, born 2004)