Lore question for the series (with spoilers for both games):
TBH because Demon Roots game came wayyyyy after King's Exit, it's likely the author haven't even thought Demon Roots characters (I think Deathpolca and Blessed Curse is never mentioned or hinted at in King's Exit) when making King's Exit.
With Bless Curse controlling the North Half of the continent, its army, a fuck ton of white phantoms and that ultra beast, its extremely unlikely that the remaining Demons even with the nursery and permanent brainwash can defeat him. (Especially with the Demons being useless against the white phantoms) In fact, I doubt even everyone from the southern continent combined can defeat him and his forces.
By my head cannon, Blessed Curse likely possessed Najezta's big bro and continued to rule as the emperor. Blessed Curse likely won't play an active role in eliminating the Demons (as Geolouise's party and savior did the major work according to epilogue and King Exit's game) and continued to rule as Emperor. According to some comments here and in King's Exit's post, Geolouise at the end of the game inherited the hero's crest and went on to become the Great King.
In NG+ dungeon, the true Geolouise/king fight is wayyyyy harder than the blessed curse (or supreme blessed curse) fight, so I am theorizing that Great King Geolouise is capable of beating blessed curse and maybe her hero's crest can prevent Blessed Curse's possession by some shenanigan. So I guess if Blessed Curse really existed in King's Exit world, it would be Geolouise who ended his reign.
Geolouise might've not gone in a conflict with Blessed Curse, but idk cause she's against slavery as we saw in Demon Root's prologue.
Ironically I think the true ending of Demon Roots is way fitting than the "King's Exit ending" as the prologue to King's Exit. Blessed Curse is that fucking op, if he were to take an active role against the Demon in the war there would be no need for Geolouise's party.