Hi Crush and family, welcome. Your future posts won't need approval so post away.

I'm sorry about the diagnosis. Are you working with an oncologist right now? If so thesequestions to ask your oncologist may help.

I'll try to address your main concerns:

my concern is, with an aggressive cancer that's been diagnosed so late, he could begin to suffer again really soon from tumours forming elsewhere.

Yes, osteosarcoma typically moves to another part of the body, primarily the lungs. It's good that his x-rays are clear. Keep in mind that x-rays won't show microscopic metastasis. If you want to have 100% certainty that it hasn't spread, a CT scan is a good idea. Otherwise, you have a good picture of where his health is right now, but not the exact one. If a CT scan is not an option, that's OK. I'd say the majority of folks go on what x-rays reveal.

 I don't think he's sleeping, he seems to be in constant pain. 

He is, guaranteed. Please ask your vet for some kind of pain control, asap. Bone cancer pain is the most extreme there is, and he needs pain control like Fentanyl to control it for now. 

Your vet probably mentioned this but please keep him as quiet as possible. There is a huge risk of a limb fracture in dogs with osteosarcoma. It's a terrible scene if that leg breaks.

How long do dogs usually take to regain any quality of life? 

All dogs are different. In general bigger dogs take longer to recuperate but they do get there. Check out our Tripawds Quality of Life Survey results to read about pet parents' thoughts after amputation. About 95% of people say they don't regret the decision, even when their dog took longer to recuperate or didn't live up to the prognosis.

Given that he will still likely die of cancer in the future (I don't know how far away that is), do you think it's worth the suffering of an amputation? I

Nobody has a crystal ball. Many dogs will out live the prognosis, many will not. It's a crap shoot and that's true with or without cancer. Amputation takes away that horrible pain. Suffering from bone cancer pain is worse, and the recovery time is not nearly as bad as you might think. Dogs take it in stride. With the bad leg gone, they move on. Most people see a huge difference in their dog's personality after amputation, as in they are happier and more themselves. It can take a few weeks to get there, but it happens. I can say for sure I saw a difference in our Jerry's personality after his amputation for osteosarcoma, for the better. And he lived two years post-op, without chemo. So you just never know.

 Has anyone here had an osteosarcoma case like this where it hadn't spread? And your dog lived a long happy life after?

Yes, there are those cases. Long term survivors aren't as uncommon as they used to be, thanks to advances in immunotherapy treatments. Dexter lived eight years post-op! Not every dog will be as fortunate, but we do see it occasionally. 

As for dogs living a happy life after, yes, things work out like that more often than not. Just look around Tripawd Tuesday stories and you'll find all sorts of great examples.

I hope this helps! Be sure to check out Jerry's Required Reading List and our What to Expect articles for some more tips and information OK? And stay tuned for feedback from others. Keep us posted.