I once spoke with the director of one of the largest research data centers in Germany, and I asked him exactly that. He said that most of the hardware would get

I once spoke with the director of one of the largest research data centers in Germany, and I asked him exactly that. He said that most of the hardware would get scrapped as there is no market for it since the required infrastructure (racks, cooling units and power supplies as far as I understood) is so specific that there’s very little use for the devices outside their original environment. That was for pretty specialized hardware of course, so it might be different for data centers that are built using more off-the-shelf components.