S5 Ending: Boyd Offered a Deal
The citizens of from manage to break/revoke/refund the bargain that created Fromville in the first place. They dig up and remember the children thereby setting them free and removing their souls from the grasp of MIY. That means no payment, so the deal is off. No more immortality for the monsters and no more God like power for the MIY over fromville. Everyone can just leave. Game over.
But it all comes at a cost to the safety of our Fromville citizens. They're in danger of being killed or perhaps have already been killed. In any event, they're not SAFE.
So Boyd is offered a deal. A sacrifice for keeping everyone he loves safe. For keeping them alive...indefinitely....