Hello, i am sorry you have this news and dilemma.
I have no experience of cancers and amputations on dogs. However, i have nursed humans with cancers, and i have masses of personal experience in making the kindest decision for my animals.
Please, i urge you not to go for heroics, cos, to put it harshly, who would you be asking to be the hero? If the dog is limping, it IS sore, and i do know that bone cancers are one of THE most painful! Animals are too good at suffering in silence. You mentioned 'painkillers until it gets too bad', how are you going to know when it is 'too bad'?? ...if you equate this to bone cancers in humans then they would probably be offered morphine....so a bit of anti-inflamatory brufen type painkiller is prob not going to touch it!! and if the vet does offer opiates - what sort of quality of life is your dog going to have?
My guideline is " rather have your loved animal put down four months too early, than four days too late" I live by this and have never had any regrets.
In Feb i lost my much loved horse to colic. He was put down at home, with me by his side. It was quick, and peaceful. the alternative was to travel him to the Dick Vet hospital (four hours away) for surgery. he might not have made the journey, and would have been in excruciating pain most of the way because the painkillers were lasting for about ten minutes. Even then he probably would not have survived the surgery, and even if he did, his life would be plagued with troubles. I loved Floyd with every ounce of my being it has torn me apart to lose him, yet the greatest honour out of the 17 yrs together, was to be able to make the decision to let him go before he suffered intolerably.
It is hard, but the love for your dog will help you though this!
Emma T