Consider that in the forest it may become unprofitable to make saws, even as the price of firewood goes through the ceiling.
well, the cutting of the tress is regulated, here, by a natural limitation: difficulty. So, the important thing is really not hash rate, but your percentage of the network. If AM is able to maintain 10-30% into the future, they will maintain mining dividend levels. Of course, selling their hardware let's them have a bigger chunk of the network percentage, effectively. Also, leasing hardware has the same result.
So, at some point, AM might have 20% of the network mining themselves, 20% mining using their hardware, and 20% mining, but leased to other entities.
By my calculations, AM has at least 180 TH/s they have yet to deploy, so just for maintaining their percentage, they should be good until the network passes the PT/s milestone (triple the current hash). And, I expect they will have more hardware in the works by that time.