SMART STATUS FAILING

Yes. Backup your files. Replace the HDD ASAP.

S.M.A.R.T. was something developed in the '90s to try and guesstimate when a mechanical hard drive was going to fail, based on observing stuff like soft errors, seek response times, etc. It does not apply in any way at all to solid state devices. As far as I know from talking with engineers from one of the top makers of industrial-grade storage solutions, there is yet no similar predictor available for SSD devices, especially consumer-grade. Yes, they fail, but the way they do so makes it infinitely more difficult to prognosticate than the old mechanicals (whose failure, barring catastrophic events, was mainly due to wearing out).

So just be sure to keep a timely and known-good backup of all your critical info and don't lose sleep over it.

Yes. At your own risk you can ignore it. One thing about SMART reports is that if it reports the drive is failing, then it usually is. Note that if you have an SSD, not a HDD, the SMART is not relevant but the report should be that SMART status isn't reported. SMART is also not reported for external drives. Maybe you should learn more about SMART before you decide whether you want to continue risking your data. But that's your choice. It's not my data.

It doesn't really matter why it is failing. What you need to do is backup your files and replace the drive.

The system is trying to warn you of impending failure. The only solution is a new drive.

This is one instance when you absolutely want to have AppleCare or base warranty alive & well covering the Mac. If you do, time to mosey over to the nearest Apple Store and have them take care of the problem.

If not, prepare for a significant hit on the wallet. The storage device in your Mac (see here for the grisly details) is not an off-the-shelf gizmo you can get at the corner geek store. Apple has decided to make it a custom component. The cheapest way to get it is by having paid for AppleCare for the Mac (or being within the one-year base warranty). Else you'll have to pony up the out-of-warranty costs OtherWorldComputing offers substitute SSD boards for these Macs, but don't know if the Late 2013 15" model is covered.

Be sure to have an up-to-date backup of the thing at all times. Even if Apple saves your butt, the Mac you will be handed back will come with a blank device and it is up to you to get your stuff back on. A bootable clone is the best option.

BTW, cool checklist, where did you get it from?