I‘m very reluctant to build up hopes, every case is different and its never good to make comparisons , however, I faced a similar situation with my last dog who became ill very quickly, his stomach swelled and the scan revealed a very big tumour on his spleen. The vet said it was most probably malignant and and didn’t think a biopsy would reveal any different. I was totally in shock as I couldn’t believe a tumour of that size had developed, to my knowledge, within days. In the end he agreed to operate, the tumour was the size of a football, but it was harmless, he recovered fairly quickly and lived for another few years.
As said, I‘d hate to build up hopes but it‘s maybe worth discussing your concerns with the vet again, if only for your own peace of mind that the decision you’re having to make is the right one for you. It is possibly grasping at straws but every dog owner does that in this situation and the vet will understand that. As to the question of the painkillers, Mudmagnets has a very good point, however Humphrey, my current dog had a very bad reaction to Metacam, caused stomach bleeding, and had to change to Novalgin.
I must add however, I have no experience of pancreatitis, my dog‘s condition was different but I have had to make that awful decision twice so I know how important it is to be comfortable that there really was no alternative.
However it turns out, I wish you all the very best and am thinking of you.