[Admiral_Young]

In Batman Beyond it was shown that Bruce was able to carry on his mission in a new way by mentoring and aiding Terry McGuniness when he realized his body wasn't able to continue to cooperate. I think it's possible for Bruce to retire being Batman, he just needs the right excuse to convince him to do so. Also in Kingdom Come he had dBat Knights patrolling Gotham City. Even in Dark Knight Returns he'd been retired for a while before resuming his role.