Like the i7-8086K, I expect they'll surpass it with another mainstream SKU, within a year.
I assume the warranty doesn't require an exact replacement. If you buy a CPU near EoL, it should still have the full warranty term - meaning they have to honor that even after they've stopped making the part. That said, if the KS is just a top-binned i9-9900K with the new stepping, then they absolutely could have replacements as long as they keep making those.
Also, how they handled the warranty of the i7-8086K should be relevant, here.