Like any infrastructure phasing out's, it will take a considerable amount of time to undo the jigsaw and mazes of frankly millions and millions of copper cabling, and as it's been cited already, when the time does come, the recovery costs in a lot of areas will out weigh the actual retrieval.
When PSTN is switched off, it will of been after a large scale switching of landline customers to VOIP Routers such as digital voice that both Sky and BT already offer, and as individuals come to the end of their 12/24 month contracts, they'll most likely be shipped a new router or switching device that will send their landline down the VOIP path via ADSL / FTTC / GFAST / FTTP.
In the case of vulnerable customers, i'm sure BT can provide a HALO Service to these customers free of charge, or other powercut type service (Perhaps a 4G Voice Sim Card?).
EDIT: I assume in the case where FTTC or FTTP is not avaliable, a standard ASDL+ service which will be used, that works on even the most distant copper EO line!
Edited by Whitehall11 (Thu 15-Apr-21 22:51:36)