From what I read in
this thread it seems like it is abusing a bug and that the enchantment should end when the mage dies. Same for:
"Using combinations of "mists of deception" + some battle enchantment damageing spell (like wratful skies) and then retreating the caster mage. Basically there is no way to kill the mist, so the enemy army has to endure 50 rounds of mass lightning bolts....".
I think we should have a house rule against abusing those spells by retreating after casting.