Looking fot a beater bike for my son for college. Ran across a converted 21 speed to SS. seller just removed the front derailleur and ran the chain through one of the rear sprockets and one of the rear derailleur rollers. I thought this would cause chain drop?

I've been tempted to remove my daughters front derailleur on her Walmart bike, but havent for this reason.

Yes a walmart bike, she hardly ever rides it. I figured that would be the case, hence the Wally bike.