NHF – new heroes for Heroes V 3.1.

In my opinion, there's no point in this. Clever players don't conduct battles like this with an army. No one will ever have more than 14 units, because wasting the entire army in any case is stupid (and a 30% return won't save the situation), and the average values between 14 units and a full army won't be that good in terms of the amount of damage inflicted on the enemy.
An automatic respawn without a tavern and with an initial non-zero army, which doesn't depend on the army the hero had before the defeat, seems more effective in this regard. Like Nicholas in the fifth campaign (but not with a thousand skeletons, hehe). But yes, this function probably needs to be disabled for neutrals, otherwise you can gather a large army out of nowhere, which would be an effective replacement for necromancy.