It is slowly dying just like the whole warband game. Why? The answer is because of the engine limitations, old graphics and old everything. In reality the game survived for a surprising amount of time thanks modding, and so did NW.
The final patch of warband and NW has already been made, and both developing companies, FSE and Taleworlds are working on new games which will be based on a superior engine with larger capability, better graphics, physics, larger servers etc.
My guess is that both public and regimental playerbase of NW will rapidly decline around the time of the release of Bannerlord/BCoF. But there are no reasons to worry, as there surely will be Napoleonic War mods in these games or maybe the FSE might make a NW game of it's own after BCoF or as a BCoF expansion.
Best way for NW to survive thought would be to make new maps which would actually be fun for public play, and new game types such as jail break, zombie attack and other