I've noticed that many people want to make sure the wildland bosses are killed means that their wildland is converted. There is a bug here that is well known to the community.
If you kill the wildland boss outside his realm the wildland is not converted. A previous fix was presented by Primal_Savage where the player may cast around the marauding wildland boss and you kill him on his tile while you are also on one of the same tiles.
This proposed fix plainly prevents the wildland boss from leaving the wildland itself (mostly). That is Vetrar, Delin, and Torax will stay within the confines of their wildland permanently throughout the game. There are exceptions to this (hence v .9) of this mod.
To use this fix you must overwrite core files unfortunately and must be installed in the location of your steam version of the game.
Steam\steamapps\common\FE Legendary Heroes
The files I replace should be backed up -- these are
I've commented the files to be able to return to the base game without issue even if you don't back up your files.
WildlandBossFix.xml --- This edits the 3 wildland bosses appropriately for the game.
T_Burninglands_02.xml --- New tactical map for my fix to work correctly
T_LombardDesert_02.xml --- New tactical map for my fix to work correctly.
I hope this fix is acceptable.