Right, it never goes to plan.
But anyway, I'd imagine if one of the top 4 guys gets hurt, then either Rodon or Lopez will stretch out to take their spot and Crochet/Kopech and the other guy will piggyback for the other start.
It sounds like they're carrying 14 pitchers and 12 hitters, as this is the only way this stuff makes sense, which means that it may be time for them to give up on Collins if he doesn't show something.