As Manhattan D.A. Robert Morgenthau belatedly celebrated his primary trouncing of Leslie Crocker Snyder in the unlikely environs of Hell’s Kitchen dive bar Siberia last week, chatter among campaign staffers centered on who would succeed their 86-year-old boss. The governor appoints a replacement if the D.A. is unable to serve, and should Morgenthau protégé Eliot Spitzer win in 2006, some expect him to let his mentor name his own heir. Candidates mentioned over the blare of “Rock the Casbah”: former state senator Catherine Abate and current state senator Eric Schneiderman. (One Snyder staffer says they were both “competing to kiss the ring” by campaigning for Morgy and that his successor will be “the one who kisses that ring the hardest.”) Schneiderman says he’s not kissing any rings and that any discussion of replacing Morgenthau would be “disrespectful.” In any case, he didn’t show at Siberia; Abate was spotted kibitzing with Morgenthau near the Playboy pinball machine.