After years of fighting physical setbacks that might have destroyed many lesser men, blues patriarch Sunnyland Slim finally eased into semiretirement last year. This will be his first gig in months; such one-shot reemergences are always a bit risky, but Sunnyland can pull it off if anyone can. At 84 he no longer has to prove anything, but his pride and determination burn as fiercely as ever: expect a vital, urgent performance from him--easy-rolling Delta shuffles, his trademark cascading treble flurries and stentorian voice, and the gruff tenderness that've endeared him to fans the world over. This should be an emotional evening, with legions of well-wishers turning out, but there'll be no pathos or sentimentality. The blues of Sunnyland Slim resonate in the present tense, and his life-affirming dedication provides the kind of inspiration you usually have to go to church to find. Sunday, B.L.U.E.S., 2519 N. Halsted; 588-1012.