Okay so I did the No One Escapes Cidnha Mine quest a couple weeks ago and helped Madanach and the other prisoners kill all the other guards and then just went on my way and everything was normal. Then last night I did the Hard Answers quest, and when i completed it I just jumped off the top right to where the waterfall hits the water in Markarth and when I sunk down a little bit I found Madanachs body just floating there. I looked at the wiki and it says that he and the other Forsworn go to Druadach Reboubt after we escape from prison, so is this just a glitch or is there a possibility of him dying to the guards after I leave?

Not a glitch, sounds like he was just unlucky and died to the guards.

Sometimes he dies, sometimes he doesn't. It really doesn't matter either way. If he lives he goes and chills in the cave and does nothing for the rest of the game.