ANN ARBOR, Mich. — Year 3 for Dusty May at Michigan was shaping up to be another memorable one. The roster May assembled, though perhaps not quite the equal of Michigan’s national championship team, looked talented enough to make the short trip to Detroit for next year’s Final Four. Monday, Michigan fans faced the stunning reality that there won’t be a Year 3 for May, who is leaving to become the next coach of the Dallas Mavericks.