Hello, I'm Dr. Deb.
I've been asked by the moderator to address your question about Zac. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
What an incredibly distressing and stressful situation for you both! I can certainly understand why you might be quite upset and frustrated.
If this were my case, I would have suggested x-rays at least 3-4 weeks after the initial examination to evaluate the leg...even if I though that healing was taking place. I would want to evaluate callus formation (evidence of new bone being formed) as well to ensure that no complications were developing such as a non-union or possibly infection.
It is often difficult to differentiate between bone cancer and osteomyelitis (infection of the bone) on an x-ray but clearly when he deteriorated so quickly, the latter woudl be more likely. He's quite fortunate to have sufvived such an overwhelming infection as you know.
In my experience, with most osteomyelitis cases, the dogs will return to normal function although it may take quite some time to do so; there wouldn't be permanent damage. Unfortuantely, in some cases, what's known as a sequestrum can develop which might require surgical intervention although it doesn't in every dog (especially if they aren't lame).
At this point, I wouldn't automatically assume that amputation will be required although this is clearly one possible outcome.
I don't know if you have orthopedic specialists available to you and I do understand how expensive they might be (compared to regular vets) but consult might be something to consider if you've lost faith in the veterinary hospital where you've been taking Zac.
Ortho cases can become quite complicated and discussing a specific case with a specialist (especially if board certified) may be money well spent.
I hope this helps; again, my profuse apologies for the delay in a response to you. Deb