Oliver has Hemangiosarcoma...

Hi all, my beloved Oliver was 100% healthy and happy three days ago, then he had a strange kind of syncope event. He went all stiff and cramped up and his eyes were flickering. It only lasted about 30 seconds, but he was very confused after and couldn't walk without falling over. I took him to the vet the next morning and they did x-rays and bloodwork and he was anemic and had low platelets (31k). They did a transfusion and his RBC's are at 40%, but his platelet count has only gone from 31k to 36k since Saturday. He has a mass on his spleen which had fluid, but has since absorbed back in his body. I have to make a decision to go with a risky surgery, which he may not survive, and the subsequent chemo and recovery, to get maybe 4-5 months more, or bring him home today and give him a loving sendoff. I'm torn apart making this decision. I can't risk losing him in surgery, but even if he made it I don't want to put him through all that. Without the surgery his tumor could rupture at any time, so I would have to say goodbye in the next few days to not risk that.
Has anyone had this situation with their dog? I'm just beyond heartbroken. He's everything to me.