OK, guys, here's the deal:
It is possible for Maltise, Eyegrim and other named enemy leaders of the specialty armies to be killed in battle, not captured. If you, for example, join a lord who is fighting Maltise, it may result in death. If you or one of your troop zap Maltise, she will be knocked out and a prisoner, and you can ransom for a gem. They were always intended to be unrecruitable, either knocked out/taken prisoner for ransom (or killed by Player, or retired by Player) or killed in battle. Depending on Player's choice of ransom, death or retirement, they might or might not respawn in the same game. If you ransomed them for money or a gem, I think there was a 15% chance they'd respawn in PoP 2.0 - 2.5, and that applies to PoP 3 as well.
It works this way because of a previous PoP 2.0 - 2.5 bug which, if you took Maltise (or Eygrim et.alia) prisoner and put them in a dungeon or recruited them, they might spawn a duplicate again and trash your game. So they are now unrecruitable.
I hope this clears up the questions - if it isn't clear, please ask again.