That's very dependent on the drive vendor, model, and even firmware version. In many cases, drives can go on working for a very long time after the SMART metrics show it has failed. Whether you want to take the "risk" depends a lot on how critical this particular device is in your infrastructure.
I have a 16GB SSD that used to be in a POS terminal before I bought it second hand. The SSD Wear Leveling Count attribute shows as failed. Still works.
I have chosen to use it as part of a RAID1 for an OS install on a home server. Waiting to see how long it will last.
It's kinda like the expiration date for foods, an estimate.
I think technically it might still work (i.e. you could read/write to it without errors?), but the integrity of the data it is storing would be questionable.
Doesn't it only mean that writes will fail?
I would think it would mean that your writes may be corrupted.
Some SSDs go into read-only mode when they have used up their endurance but others will let you keep writing.
It should but due to crappy firmware many SSDs will just drop off the bus and become unreadable.
In production tests I've seen the synthetic "wear out level" go down to 1% and the machine still writing Petabytes of data without any issues. That being said, I would only do that on machines that are mostly disposable :)