Mayan Palace, as far as I know, does have a brunch. We were out there not too long ago - didn't eat this time but were shown the buffet and it was pretty extensive. Lovely setting. Know Mare Blu's food is good, although haven't tried their brunch.
You hit the best choice, flash! Can't beat that beach view as you're leaving town. You're lucky you didn't stay in town until happy hour, it happens often! Come back soon!!!