Although I haven't gotten around to reading the whole thread, I have read the last couple hundred posts.
I advise that the maze, whatever it is, IS winnable, but the exit moves every time someone uses it, and maybe more often.
Even better if the maze itself morphs over time, such as every 5 minutes, so that anybody within it has to get VERY lucky to find the exit in time, and due to the exit shifting when someone exits, greifers cannot maze-team and all exit at once.
Additionally, add fake walls.
And invisible walls.
If thise also shift, they would force a player to explore every dead end carefully, on the unlikely off-chance of it leading to an exit-path.
Trust me on "unwinnable" mazes, I once made one in the alpha of blockland, where it was basically a grid of mostly-transparent walls, some passable, some not, grouped into semi-maze-like blocks with "doors" that would teleport you elsewhere. To finish, a player had to navigate to the right door for each section about 10 times, with ANY mistake bumping them back, usually to the start, or sending them to a false path/dead end that then lead back to the start.
I let players wander for around an hour before showing someone the way.
And it was on a 20x20 grid or less, if I recall correctly.
50x50, with a moving exit, and morphing/shifting walls? Impossible, in practice, while solveable in theory!
Note: blockland is a first-person game, further confusing participants, as at each door they would lose all sense of location. If they lost their direction, even momentarily, and couldn't recreate their location/direction from their surroundings(IE didn't create it), they were doomed to restart.
In fact, if I still have it lying around, I could host it for your entertainment, or at least create an overhead map as an example.
Interestingly, there already are fake walls, that you have to click multiple times to open. That way, to find all doors for sure, people would have to click every single wall 5-10 times.
As for the shifting maze and exit idea, its definitely possible, but I'm not sure how easy it would be...
Also, you have the alpha of blockland? Does that even still work?