I guess that in the case of a downfall of AI where the datacentres has to be closed, they will sell the whole centre or at least their computers (or components) to other kind of datacentres...
Lots of those computers won't be used for anything at all, so it will probably be sold to different companies that could make use of the spare parts for the low cost, but even so, many components as RAM will be sold to companies that sells them to people, probably in Aliexpress or Ebay, but most won't be any usable for you, ECC RAM, server motherboards and CPUs that require them... Not to talk about hard drives, they will all be disposed. But good news are that it is known that some servers use regular RAM emulating ECC RAM with Linux, that will be something you could use! But for the high demand it will have, I don't think it will be that cheap...
However, new components won't be sold to those datacentres anymore and many companies made so much money with this bubble that it will be a really good and huge change for the market of new components.