Giving Haven to other Lords: faction and vassals
If a (friendly) faction is defeated, have an option to 'save' the Legendary Lord (LL) before they are killed.
(Inspired by Three Kingdoms mechanics)
Player is Empire-Fraz, and Volkmare is defeated. Have an option to save his life.
This could be done as a vassal, or an auto-confederation.
High Elves, 'save' characters who are across the map that you haven't been able to get to before they are wiped out.
LLs are strong enough to escape the loss of their faction, which is why I don't recommend this for non-LLs.
Costs: Gold to 'save' and bad diplomacy for anyone the saved-character was at war with.
For vassal-ed characters: you could give them a/any territory you own, or force them to 'wander' till they conquer their own territory. The choice impacts how much they like you while a vassal.
Maybe this is a specific type of treaty you can sign between factions?
Maybe it is auto-set for other factions of your race?
Maybe you get the option to decline and let someone die that you don't like?
Being at war with the other faction of the treaty doesn't break the treaty.
Aversion-factions will be harder to make this treaty happen? High Elves and Dark Elves wouldn't save each other.
Is it weird to know about other members of your race who are still in the fog-of-war? (hidden elsewhere on the map)
I have had Dark Elves basically do this against me in campaign, which is why I thought of making it an option for everyone. They faction-ed across the world and I had to go hunt down the last remnant of their faction to win.