Is there any way to extend the lifetime of a SSD by allowing its capacity to decrease by replenishing its reserve of replacement blocks so that the SSD could continue to operate until it runs out of writable blocks?
A zoned SSD has an explicit mechanism for the drive retiring zones from service and making them read-only or completely inaccessible. But it's not currently practical to use a zoned storage device as the primary or sole storage in a system; at a minimum you need a regular block device or namespace to boot an OS from.
I don't have hard data however on like the "curve" of flash cell failures as an SSD ages and therefor exactly how much longer you might get based on the minimum to median cell failure.
I think most OEMs opt not to let you choose this sort of thing and rather bury it into the drive firmware.