Nope. Directors aren't required to be there at every performance. A director just leaves the floorplan, as you will, and the stage management and the other creatives call the show every day not the director. For example, back when the Spring Awakening tour was still happening. Michael was dealing with Idiot which was just starting on Broadway. However, the second to last week of the tour, Michael went down to see them leaving Idiot running fine.
When I said 'previous engagements,' I meant family or personal time like when he took time off for his cousin's wedding back home in Delaware. John is a major draw for the show. I know that people have requested a refund when he's been out, even if he's not above the title. So it was be a negative thing if he did the panel instead of the show.