Eight is not that old. They can live twelve years or more if well cared for; I do not think palliative care has to be the answer. That's like not treating a person's cancer because they're 55. I am not a vet, so I could be wrong about how bearded dragons tolerate surgery as they age, but I am skeptical of this vet's conclusion. My beardie had a liver tumor on her bile duct, and if this is the same kind, it kills them if not removed. I would seek a second opinion from another vet if you can, because even if the surgery is higher-risk, it sounds like a choice between a surgery that might kill him or a tumor that will. My beardie had surgery to remove her tumor. The surgery went smoothly, she recovered well, and the tumor has not returned. Unless there are complicating factors you have not shared here, a good reptile vet should be able to remove a liver tumor.