Hello, and welcome, Kate and very handsome Jag! Very glad to read your update; it helps so much to know just what you are dealing with, and you got really pawsitive news! 

Every dog is different, and every day can bring a new challenge, but I have no regrets about the rear leg amputation for my then 11-year old Samoyed/GSD mix, Princess Roxie.  She was diagnosed with osteosarcoma in March, surgery was done the next day, followed by 6 rounds of chemo.  The onco told us she was already essentially a 3-legged dog already, and she was hopping full-speed ahead 2 days later.  We were very fortunate that she had a speedy and uneventful recovery from the surgery and was able to soldier through the chemo with just some appetite issues.  We'd hoped for a year (a very big deal with an older girl), but the cancer spread to her lungs, and she passed Tuesday at our vet's after 6 months of shameless and extensive spoiling. And she had a very hoppy 12th barkday party on the 1st of this month. Most important, the pain left with the leg, and the change in her personality was amazing; they told us the surgical pain was nothing compared to the bone pain she'd endured. 

It sounds like you've got brighter days ahead with your Jag, and much support to be found here.  We'll look forward to cheering you on!

-Liz and Angel Princess Roxie