Oh man, you just broke the game. I just tried it, an you're right. Excellent find.
So, if you just fight Balrog and go back down to booster, even if you feed the cure-all to him, then he won't be able to recover, and will tell you you're too late, and die regardless of whether or not you had the cure-all. That is, if a certain flag is set after you fight Balrog. Apparently, this flag gets unset if you continue on through Labyrinth M, allowing Booster to recover. I commend you for discovering such a massive glitch, but I'm afraid that the final version is out, and that I'm done working on this mod. Any glitches in this version will stay there no matter how game-breaking. I'm afraid it's too much work as well as too late to fix this glitch, make a new release, and then have andwhy re port the new version, and have everyone replace their games with the new version. I salute you for the bug report, but I'm afraid it's too late to fix it now.