Two sisters.

The ability for dwarves to flee the battlefield was also disabled in the latest version; I don't remember the exact reason, but it was discussed in this thread (most likely, in certain game situations, they fled too often, without even properly fighting).
Regarding limiting the ability to flee to only the four main heroes – it's a good idea, but I probably won't be able to implement it at the moment, as it's no longer possible to change or modify anything in the map.