besides turning her evil and becoming a loyal force sensitive alley what do you guys think maul needs her for? i know maul wants to replace what he had with his brother savage with someone else but besides that, I think he needs devon to hunt down and use sith/jedi holocrons. only force senstive beings can use them and we know in rebels he was trapped on malachor the sith homeworld in search of one, i imagine this where the story is leading, him and devon somehow make on malachor but their ship gets destroyed devon dies somehow and that leaves maul trapped on the planet forever in search of the sith holocron and in hope that someone will come along and he'll escape. it wont be until ezra comes along that he's able to do just that.
i think they'll either do this or just focus on the whole intergalactic crime stuff.
There's also the possibility devon could betray maul and leave him trapped on malachor, but then id have to ask where was she during the events of everything else that takes place after? did she just decide to become a hermit on some small planet, like how luke was in the last jedi.