%&@$# ! Fliping ridiculous!
Turns out that immortals do rout after 50 turns regardless due to the battle duration rout rule. But here is the kicker! If they don't get off the battle field before the end of 25 additional turns, they DIE (as in dead). Who cares that they are immortal? It is as if hanging around on a battle field for 75 turns surrounded by mosquitoes is somehow a worse fate than being run through by a sword, disintegrated, soul slayed etc.
Oh well, looks like Agartha is toast in this one.