Dear notrailends,
I have never heard of a situation where "the ball should fail", although I suppose just about anything is possible in this life. The more likely scenario would be that a trailer hitch comes off the ball when not properly seated or locked in place.
Excellent discussion has been provided to factor into your travel preparation. However, if you want a fail safe solution to the possibility that your hitch may come off the ball, buy and install a TRAILER GUARDIAN. Check their web site:
www.trailerguardian.com
Good luck and safe RVing.