I'd go back to motorcycling, competing in observed trials. Obviously not an option for someone with back problems as it involves a lot of falling down and picking up motorcycles. Low speed falls and light motorcycles, but that would still be a problem.
Besides that, any other form of motorcycling, building/rebuilding motorcycles, farming, spending time with my wife.
But to be honest, I'd work very hard to come back to cycling. I need a lot of exercise to be happy and I am really enjoying cycling at the moment, even though I am cat 4 pack fodder for most races. Doesn't Lance have a bunch of fused vertebrae in his back?