Yes, Michael Rosenbaum has succumbed to the pleas, entreaties and, possibly, threats from Smallville fans and will, indeed, appear in the series finale.
According to deadline.com’s Nellie Andreeva, Rosenberg is quoted as saying, ‘I’m simply doing it for all of the fans out there who made Smallville the great success it is," he said. "I appreciate all of their passion, their relentlessness and even their threats. Ha ha. I can’t wait to hug the old crew back in Vancouver one last time and see all of my old friends once again….. Oh, and for Lex to become the badass he’s destined to be.’
I sure I’m not alone in saying, ‘Woo-hoo!’