I think it's pretty easy to nip the escape plan part in the bud. I mean, the powers were given to them by someone who has the ability to hand out powers. I would just go ahead and assume anyone handing out super powers for a game and a few lols would have some pretty intense stuff hidden up their sleeves. Omega powers, the ability to have the powers removed or only active within a certain area. You could explain the lack of escape a million different ways. "There are atom destruction rays pointed at the perimeter of the playing field and anyone attempting to cross will be removed from existence." "There are omega level powered guardians who have the power to warp reality and just move your character back into the play field." "The powers are activated by an ultrasonic frequency. Moving out of the play range, and the range of the sound, removes all abilities and leaves the player weakened as they adjust."