My adult dog Booker had part of his tail amputated recently... I posted about it here with some photos.
It wasn't a complete dock, he still has half his tail, or a little more. The vet did a good job putting it in a protective cover with a plastic tube post surgery, and Booker had an enormous e-collar. He actually didn't mess with it at all, surprisingly... it had bothered him a lot before amputation and the bone broke and was visible through a deep wound on the tail, so maybe in comparison some stitches and bandaging were a relief.
In fact after getting the tail re-bandaged twice in 5 days (it kept coming off from him wagging!) I just removed the bandaging, the bandage was meant to let air flow around the stitches anyway, sooo..... I just kept the whole area clean and dry, and again, shockingly he didn't mess with it and had the stitches removed with no problem. His fur still hasn't grown back 100% and this surgery was done in the beginning of February.
I am so sorry to hear about the lab results. I hope for a speedy surgical recovery, and of course NO return of the lumps, for you and Tiva!