A dev declaring that his game is abandoned is NOT the same thing legally as stating that he has abandoned any, much less all, copyright on his work. In fact, a dev could say that he welcomes others to pick up where he left off and he STILL could retain copyright of his original work. In order for a dev to lose copyright they MUST declare that their work is open source. Unless they do so it is assumed to still belong to the original author.
A case could be made for abandonment if and only if others copied his work without permission and the dev declined to enforce his copyright. An ongoing example of this would be the fan work on trying to resurrect the defunct HTML game SQ Cruise Ship, where the original dev has been incommunicado with anyone for 7+ months. In the case of eWardrobe, the dev is still in touch (more or less).
You work in gaming, don't you?
This would be true under most contexts, but IF a dev states they are abandoning a project and not taking an extended hiatus this would constitute legal abandonment. Brick said he was abandoning it, he was never returning to it. Now, this might have changed in discussions on his Discord, but as it stands this is an abandoned project used under a GPL licensed tool. Is it a clear-cut case? No, but if someone were to take the project up, as stated above in the thread, and title it "Fan Remake/Continuance" they would have standing to even profit from it.
Brick would then have to take the case to court, dox themselves, and show how he was damaged in his copyright claim and how his statements of abandoning the project were not true. He would have to show this, just saying he didn't like how the project was taken or how he now wants his monies would not be good enough.
In my opinion, I don't think he would care since it is clear that a long enough time period has passed without him communicating any interest in the reuptake of this project.
edit: Also, if he did want to return t it, I don't think anyone working on it would mind since he is the original author and most of us would love to see how the story turns out.