Hi Wendy:
I'm not trying to scaremonger because ultimately you must be guided by what you think is best. However, 7 years ago our elderly collie, 14, had a huge benign lump the size of a bag of sugar on one of his thighs. He'd had them over the years and had had them removed successfully. This time, though, he was much older and we were reluctant to have him operated on.
Anyway, after consultation with a junior vet, and much against our better judgement, we allowed them to operate. I took him in, went home, and less than an hour later got a phone call from the vet saying that he had passed away under anaesthetic.
Needless to say we were devastated, but more than that I had an overwhelming feeling of guilt which has remained with me to this day.
I most sincerely hope that your outcome will be far more successful. Very sorry to hear of the loss of your other doggie.