The servers may well be worthless (or at least worth a lot less), but that's pretty much true for a long time. Not many people want to run on 10 year old servers (although I pay $30/month for a dedicated server that's dual Xeon L5640 or something like that, which is about 15 years old).

The servers will be replaced, the networking equipment will be replaced. The building will still be useful, the fiber that was pulled to internet exchanges/etc will still be useful, the wiring to the electric utility will still be useful (although I've certainly heard stories of datacenters where much of the floor space is unusable, because power density of racks has increased and the power distribution is maxed out)