So at the request of fellow forum-goers, who were sick of going back to the beginning of a level after the marble fell, I hurried up and added restart zones. So far they work out quite well. At first I just had restart “points” and when the marble fell, whatever point it was closest to on the X/Z axis would be the spot to go in. But I starting playing with it and saw an inherent problem: the player could end up restarting where they haven’t been yet (?). That doesn’t seem right.
I have since changed the concept to a zoned restart point which means once you enter the zone of a restart point (approximately 5×5 tile area) it is available for you to restart in. Restarts are widgets and widgets can have zones, so this easily fit into the current system.