Once a diver allows a free-diver to breath off a reg at depth, that diver becomes obligated to see the free-diver safely to the surface.
The free-diver does NOT need to breath consistently off a reg. What they do need to do is to keep their airway open as they ascend. This is no different than what every diver is taught in OW, don't hold your breath on scuba, and once you breath air at depth, you become scuba.
If a freedivers shows up and grabs my reg, I'm going to help him/her. However it they choose to bolt to the surface, I won't follow at a speed faster than prudent. Better one hurt diver vs. two.