You can always get up to Infinity on YieldFarmer2

But are the stairs a softlock?

loved the game until I entered the stairwell and was not able to proceed or go back. Having this as a softlock is sad, especially since this could be a continuation of the story by using the stairs as some kind of emergency exit

I was thinking that if I ever do an expansion or DLC, then maybe you'll be able to open the door to the roof.