I agree somewhat, but I feel like there's also a bit of a difference here. Literally nobody knows where she's being kept. The closest to knowing is that Jena realizes they were succubi taking her. But as the game has shown, there are multiple monasteries scattered around the separate realm where the succubi live, so finding her would be nigh on impossible in this situation.
However, I do wish the MC would more often ask about whether there were progress, express emotion at missing her, etc. The fact that this isn't really done does bother me a bit; if you're trying to show an emotional connection between characters, they should show it more. But I don't think the MC should go off trying to find her. He is from earth and knows next to nothing of other realms; he would only get himself killed trying to find her. If Demi did eventually get rescued, then, how devastated would she be to know her lover-son is no more?
What's more, the entirety of the Red Queen's people would lose their current incarnation of Ducarius. From the sounds of things (based on what the Abbess said in this release), I don't think the Red Queen has time for another rebirth of Ducarius to happen. And, like the Abbess says in this release, if the Red Queen's people fall the Hellions will march on everyone else eventually. Earth itself is probably also at risk of being lost. There's too much at stake if all of existence is going to be lost.
I'm in no way happy about Demi's situation, but I do think it's too easy to jump to the "rescue her now" mindset. I feel like there's literally nothing that can be done by Ducarius, Jena, or the Red Queen's people. Personally, given some of the things revealed in this release (as has been already discussed on this thread), I would expect that Soreana will eventually defect entirely and bring Leeta and Demi with her.
So Demi won't really get rescued per se, but she'll be returned during that and eventually get back to Ducarius. I think this would easily solve the problem of no one knowing how to find Demi while still getting her back to her old life. That comes, unfortunately, with succubal addiction/enslavement and extreme mental trauma lingering for . . . well, possibly forever.