when the bike is making a correction, it can overshoot and then stop the wheel suddenly, which would ultimately result in the bike becoming perfectly upright and the wheel not accumulating any speed from one correction to the next.
if the momentum of the correction you need to make is greater than the momentum of the wheel spinning at max RPM, then the bike will fall over. this means that the system will fail if the bike is pushed too hard, becomes too off-balance or if there is something heavy, like a person, on top of it. with a wheel that was heavy enough, and a motor strong enough, the bike would be able to make itself upright from laying on the ground or keep itself upright with a person and cargo on top.