Re: house of cards question
It could be used for another cryptocurrency
It could be used for any other need to process sha256 hashes
Or, more likely, the machines will be scrapped. Despite the ostensibly large processing power (from the specialization), the number of actual machines is rather small compared to all the consumer computers out there.
Already there are 4 generations of sha256 asics out there, 3 of which (probably but 2 for sure) are currently obsolete, not worth using any more.
I guess what happens to them is the same thing that happens to all those decade+ old laptops and desktops.