Lucius told Zenon when he ask for the demons power after the lost of his friend, Lucius then explains his plan to use their demon's powers to remake humanity with undying bodies in order to create peace.

Meaning he needs Zenon and Vanica alive, Dante is not necessary due to the fact Lucius now has his demons power now. 

But, Zenon may not want to do that again, he may join force's with Asta and Yuno, and apologize for attacking them, which of course Asta will except because he forgives everyone.

Vanica most likely won't turn over, because she like's to fight and kill, but I do see Zenon turning over a new leaf, and fighting for the good of the world, he may even help Asta use his demons to fuller of it's power, you'know because Asta looks like Allen, Zenon's friends.

I think it would a really nice turn events. Well tell me how you think this theory is.