I'd like to see Lycanthropy (and possibly Vampirism) being spreadable even when the original carrier dies in battle, or when either of the combatants withdraw.
Lycanthropy might have a small chance, higher the more damage taken from battle with a werewolf and maxing out around 10% when taking ~99% damage, for the surviving opponent to turn into a barbarian-controlled Blooded Werewolf. Further, Duin and any Greater Werewolf could, always successfully, convert these wild werewolves to their cause when engaging them in combat.
Vampires, next, might perhaps spread their condition when wounding enemy units of level 6+, but leaving the new vampires under the control of their original owner - allowing others to use vampirism. To make sure the Calabim profit from it as much or more, however, have the Vampire Lord unit, as well as Losha Valas, insta-convert any vampire of lower level than themselves when engaging them in combat - possibly with a minor chance of failing and getting a regular battle if the convert-to-be was affected by loyalty.