"Give him a choice. He can stop this, and undo the spell he's cast, or - he can be contained. Forever. In a universe of his own making."

He felt the creature hiss and struggle. "That or you can at least have some things to amuse yourself instead of the nothingness and vastness of space."

He didn't think this Stephen would want to - help. "Think of this - there is a future, for this world, where your sister would be reincarnated, properly. There's also multiverses where ... she's still alive, perhaps - that you could keep from destruction. There is not the "no future without her" that you currently feel. It is a Fixed Point, not even you can change that."

He can tell what was once Strange might be torn over this. It's a pity his soul is so corrupted, that even splitting it would be risky.