Your doctors might never be asked any questions by SS. If you have them state that you'll return to work if your SSDI benefits are terminated, that means you have the physical ability to return to work and should. (Asking your doc to put that in writing is a BAD idea IMO. )
It doesn't matter if you have a job or not, it's the ability to work that matters. SS makes that decision, not your doctor because it is a complex medical/legal determination. --If your doc is not supportive and SS questions them, you'll likely be terminated.
Frankly, at your age, it would be surprising to be terminated, but it does happen.
While the rules do allow you to collect the 9 months pay and SSDI, returning to work will often trigger a long form CDR. If they determine your condition has improved, they'll terminate your benefits--which gives you 3 months more before you're cut off.
http://www.disabilitysecrets.com/res...ng-reviews.htm
You might want to take a look at the Ticket to Work Program as well. It gives you additional protections such as being exempt from a medical CDR. While your job was physically demanding, they might be able to help you find something with fewer physical demands or even have you answer calls from home.
http://www.ssa.gov/work/overview.html