These drills are meant to train the core and stability muscles to recognize "uh, oh!" the second you get out of balance, and recover back into balance, before the bobble becomes a full-blown fall.
Knowing when to recover, and when to let go... well, that's beyond my expertise at this point. My suggestion is to listen to your body, and utilize those well trained core and stability muscles to hold and get back in balance quickly. If it doesn't happen, let go, and take the tumble!
Here is Liat doing the backseat version of this exercise. The medicine ball is behind her to represent the force pulling her back in the fall, and her leg has come up in front of her to compensate. Now we freeze.
She stands holding the position as quietly as she can, strengthening the recovery muscles that she will need to engage should she get into this situation on her skis.
This is video #2 of many exercises like this on the Bosu ball that simulate falling recovery. Try it out! Discuss! Tell me what you think! Tell me if you want more!