Just allow the goal in your book to expire. I know it's a nuisance to see it in your book, but it will disappear at the conclusion of the event. Your sawmills will provide plenty of wood or even better, chop a dead tree or other log item where you don't have to grow a tree. I think this is an excellent compromise and essentially gives players 3 days back as you don't have to wait for requests to trickle back to you.