If parks reach capacity, they will do so early in the day and then they will begin to clear out by late afternoon. If you park-hop, just realize that you may have to hop to a park you weren't planning on hopping to! But even then, you can usually get back in if you just wait a few hours and go somewhere else.
However ... even if something DOES close at capacity, it's usually MK. MGM and Epcot have closed rarely, and I don't believe DAK ever has except during its opening week.
Dreams Unlimited Travel is committed to providing you with the very best vacation planning experience possible. Our Vacation Planners are experts and will share their honest advice to help you have a magical vacation.