I've been playing HoMM3 an hour ago and came up with the following indea =) :
Concider the following example: I always need an extra hero following mine in case of Fortress, because when I go for dragon fly hives, i need to kill monsters guarding it and then enter the hive only with Hydras, so that i do not loose anything. These little dragon flies will eat poor gnolls ALIVE!!! I propose the following:
1. You can select which monsters participate in the battle, which don't.
2. All that do not participate, perish if you loose against the moster.
3. If you are fighting a hero, and you loose, enemy could have a possibility to catch running monsters and fight them.
It might only be more interesting to play, because of new tactics. You can select only fire immune monsters and use armageddon, during the battle... Let's hope that the enemy does not have any artifact that blocks magic. Or maybe you can leave some of you monsters not participating in battlefield, and then split the fast monsters so that enemy does not retreat. Could be interesting, what do you think?