I know several horses eventing at training and higher with old, cold and set bowed tendons that do not bother them in the least. I have another friend whose prelim mare tore a suspensory about 2 years ago. They spent the better part of a year rehabbing her and she did come back and return to her previous level of competition. Unfortunately she suffered a second torn suspensory this spring (different leg) and she has been officially retired.
I think as long as you properly condition your guy and really take you time, I don't see any reason why you shouldn't be able to do some lower level stuff. If he hasn't been jumping after his injury I would make sure that bringing him back everything was done really slowly and gradually, to build everything back up. Lots of long slow distance work, so lots of walking and trotting will help, starting with shorter distances and then slowly increasing as you go. Muscle is the quickest to strengthen, then tendons and ligaments, and then bone is the slowest to develop.
Cold hosing or icing and the wrapping after jumping or a hard ride would be a good preventative, and getting your self REALLY familiar with every inch of your horses' legs is never a bad idea! If you can notice every little bump or bit of swelling when it first pops up you will be way ahead of the game, give him a easy hack day or a day off if his legs have a bit of fill or are a little warm, stuff like that. I'd be extremely meticulous and picky about the footing as well, avoid hard/deep/sticky/muddy if at all possible, at least until you know for sure he is good to go and you are back in business. So I would say for the first few months at least, until you've got a good base of conditioning and fitness back.
And you'd just have to listen to your horse. If he's coming out with cold, tight legs most of the time and seems happy and wanting to work, then that's good! If he's coming out with heat and stiffness, or a sour attitude, then it might be too much for him. And of course, if any problem crops up, you'd want to get the vet out asap to evaluate. Ideally you'd want to be bringing him back under the supervision of a knowledgeable vet and trainer as well, but I know that that may not be totally feasible for some situations.
Hope this helps:)