For "end of life" I mean when some of the SSD cells won't erase anymore, and the S.O. starts complaining about write failures.
When this finally happens, will I still be able to safely copy all of the data without any errors?
And if I don't replace it soon, will it ever stop working? (for reads only)
Firstly, it's a bit of a myth that SSDs will wear out, especially for typical desktop use. But anyway:
From another superuser question:
In theory, it is possible to read data even after all program/erase (p/e) cycles have been used up. In fact, the JEDEC specifies that data on consumer-grade SSDs should be readable for one year after all p/e cycles have been exhausted. So the likelihood of losing data due to the drive reaching the end of its lifetime is small; it's more likely that you'll have replaced or upgraded your system by then.
And here:
Second, when an SSD is allowed to run right to the end of its useful life, most controllers put the SSD into a “Read-Only” state that allows the operator to remove the SSD, copy its contents onto another device, then re-start operations in the shortest amount of time.
So you can't write on it, but you will be able to copy its contents to your next SSD/HDD(for a reasonable amount of time).
