A Proper Journey’s End
In the great Dawi-update for Total War Warhammer II CA gave Ungrim Ironfist a Lord-specific ability that gave slayer-units in his army the Journey’s End passive, preventing them from losing models until the unit HP drops below 50%. CA toned down the ability to shut off at the 75% HP threshold in a later patch.
I say no more!
Welcome to the days of Journey’s End once more lasting until the 50% HP-mark! And lads? I think I smell Trollstew on the wind!!!
That’s all this mod does and should as such be compatible with almost everything; if a mod adds more slayer-type units it simply has to add those new units to the dwf_slayers unit set and things should function for those units too!
EDIT: It was brought to my attention that this mod can sometimes refuse to work even when it should. In such a case I would recommend using the Community Bugfix Mod as it contains a lot of fixes, the "entities_can’t_die"-mechanic among them.
P.S. The Community Bugix Mod might not be needed as of patch 2.3, but now you have another possible solution if it refuses to work for you.
Image credited to AlexBoca at DeviantArt:
https://www.deviantart.com/alexboca/art/Dwarf-Slayer-678681097