You can stay in the park. There are various locations in MK where you can pick your wrist bands up after around 4pm. We collected ours from the shelter in by the river in front of Tomorrowland. You show your
MVMCP ticket and they mark it to show you have recieved your wrist band.
Then at normal park closing everyone with a wrist band will be directed to wait in the park - we had to wait in a roped off area at the hub in front of the castle (CMs came by quite often to check for wrist bands).