The Beast meets in his study (the room with the breakfast and lunch ordering kiosks) so after dinner on your way out you can have a photo op with him. He does not sign autographs. If you have a very late dinner they announce in the dining room that the Beast will be leaving to give all the remaining dinner guests a chance to meet him.
Intermittently he will walk through the dining room on his way to or from the study, but he does not stop at any tables.
While Disney will not guarantee that he will be there because there is always the possibility that he might become ill or something else can happen during the evening I haven't read any posts that someone didn't see him because he wasn't there that evening.