In my experience, if you are stronger and have an heir they'll come back around eventually, reloading the game may help. Don't marry countries that can claim your throne (same dinasty) when you don't have an heir, also invest your favors in trust (maintain a base 10 favors). I always desinherit Enrique and try and ally Aragon, so nobody messes with my future land, but you can't marry them then.Also how long until the modifier goes away?
Until they lose their restoration of union or enforce Union cbAlso how long until the modifier goes away?