Never dropped a crossover chain; but did break one a couple times.
First time we were just leaving a motel while on a tour and that was an easy fix.
Second time was less than a mile from home. Stopped, picked up the chain and stoker Kay pedaled us back home while the captain coasted and steered.
BTW Kay has 75% lung capacity and has ridden/climbed at over 9,000 ft. elevation in our 'younger' (read under age 65) days.
Keep the eccentric properly adjusted to avoid chain drop.
Pedal on TWOgether!
Rudy and Kay/zonatandem