Ozzy Osbourne, with Korn, Monday, December 31, at McNichols Arena, has reneged on his retirement, and who can blame him? During his gory days with Black Sabbath, he was routinely pilloried by social watchdog groups, and his music was sneeringly regarded as boneheaded spook-house fodder by mainstream critics. Now, however, the Sab sound is back in vogue (Pacific Northwest acts such as the Melvins often resemble Ozzy cover bands), and even snooty reviewers concede that Osbourne's brainchild was among the most influential combos of its era. Ozzy's comeback platter, the not-so-wittily dubbed Ozzmosis, is pretty weak, but that's a minor drawback. After all, how often do you get to bring in the New Year with "Iron Man" bouncing around your head?