We've been checking in on the SSD Endurance Experiment for a few months now and they have just crossed the 1,000 TB write milestone. They started with six different SSDs and now they are down to three. If you are concerned about wear-leveling and TLC and MLC endurance, you really should check out this article as it shows drive failures in the real-world - not just hypothetical.
Continued write cycling eventually causes cells to become unreliable, at which point those cells are retired and replaced by flash harvested from the drive's "spare area." This reserve of fresh flash area ensures the SSD maintains its user-accessible storage capacity even if cell failures incapacitate some of the NAND.