I’m curious, do you really think Innie Mark is stupid? You’re right, there isn’t much hope for him if he stays on the severed floor, but it’s either that or, for all he knows, death😭 considering what he’s done, he’s fairly positive Lumon won’t ever let Outie Mark come back, and (as shown in the camera scene) he has his doubts about reintegration. In his mind, if he left he’d A) likely never live again, and B) even if he did live again, he’d definitely never get to see Helly again