Not quite how it works. The SSD will never have a capacity lower than its rated capacity.
For the failures I've seen, once the SSD goes to do a write operation and there's no free blocks left, it will lock into read-only mode. And at that point it is dead. Time to get a new one.
Now I'm really curious. I took the drive I swapped hundreds of terabytes to, and put it in a server (unfortunately not running a checksumming filesystem) and it ran happily for a year.
For the failures I've seen, once the SSD goes to do a write operation and there's no free blocks left, it will lock into read-only mode. And at that point it is dead. Time to get a new one.