I think technically he should retire because I dont think he can beat the best in or around his weight division. But I mean he could probably still beat some good guys and make some money, but his top flight days are over.
Theres only two main reasons that should keep Tarver in or out of the ring.
Health & Money. If Tarver can get some good money for a fight he should continue, but not if he feels his health maybe jeopardize.