When I say the Spen will die I mean that if they make it an accessory to the note like they did the s21U instead of built in like the note series, the Spen stands a good chance to die. If people don't buy it, the Spen will die. Note users have become accustomed to a built in Spen, why would we want it a carry around.
I myself do not think samsung will release a stand alone note with the S series, I think it will become part of the S series, S ultra will be the note. I think that is why the S21U has Spen support, it's the transition period, even though IMO they botched it up by making it an accessory. The article says they are going to continue building on the Spen experience, they didn't say they were going to release a note next year, that could mean transition over to the S series.
Either way, right now it's just theories, we will have to wait til next year to see what they actually do. I just put a theory out there, who knows what samsung will do.