Back up map runners.

Having a seventh or eighth map runner that can automatically substitute in when one dies preventing the map chain from stopping.

Understand it is slightly complex because it can change the fail probability, maybe drastically if you loose high level runner and have a low level sub, but would be the choice of the player. Would not have to allocate subs.

It would still fit with the town population limit which is 6 extra, 2 subs per map, and decision on whether it is worth having these versus flexibility in other areas.