If that does come true, which honestly is more likely than not, then I'd probably drop the manga too, given the fact that it'll be very predictable from then on.
I hope it doesn't come to that, but I've been burned too many times and come to recognize that most manga, when given the chance to break from the traditional/expected/common will ignore that and just do what everyone else has already done.
maybe it won't be demons (I don't even know if something like that exists in this universe) Maybe it'll be shady scientists, or some sort of anarchist assassins, or people plotting to over throw the kingdom, or some rich noble that wants one or more of the girls from Rainbow Butterflies for himself, or whatever. But chances are that we're gonna get:
1) Judal gets out of prison, either by breaking out or by someone using some influence/pull/subterfuge to get him released
2) He declares that he's going to crush Makina because everything bad that's happened is his fault
3) Whoever else is involved somehow (either they approach him with an offer if he broke himself out of prison, or they rope him in as a payment for them helping him get out if they did) offers him the opportunity to take out Makina and some sort of super-shifty power boost or weapon to get it done
4) He greedily takes it without questioning the fact that ti's the world's most obvious trap and runs off to confront MAkina, probably mouthing off at the people "helping" him in the process to hammer home that he's a self-absorbed jerk (who can't back it up. Because
that is the unforgivable sin in manga. Not that you're an asshole to people who don't deserve it. That you're an asshole who isn't good enough to excuse your arrogance)
5) He temporarily gets the upper hand, but Makina turns it around because he has friends and because Judal is an idiot who doesn't think ahead, letting him be easily manipulated
6) He gets beaten down in teh end and defeated, at which point his benefactors turn on him and either leave him for dead or reveal that htey figured he would fail and they had some sort of failsafe in place that would probably kill him in the process of also trying to take out Makina (like the weapon he was given is a bomb or something)
7) in his final moments, Judal recognizes that he's gone off the rails and become a dishonorable, detestable person who has done all this for selfish reasons. He then "forgives" Makina and Makina in turn shows him respect that he absolutely doesn't deserve as he dies. Then we'll get Makina remembering him as a good person in spite of the fact that we never saw anything close to that because even his "better times" flashback that we just got still showed he was an egocentric knob who made it all about him.
I've just seen it too many times. As evidenced that I can lay out a precise 7-point roadmap as if it's nothing.