The rabbits we take in that have been outside and trying to live on their own for any long period of time are usually not in very good shape. Start looking, putting up signs, and trying to trap him. The longer he stays out, the less chance there is that he'll come back.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry