IMO it'd be healthy and would benefit the game if there was a new world annually. Especially if there would be a set date (i.e. August 10 every year) for a new world to start.
That's not a secret that every time the word was reset along with a major patch - the numbers of players online grew tremendously. And with the world aging, the numbers lower. Why so?
- The world becomes exhausted: natural resources are dug out, best spots claimed, lots of terraformed abandoned places that are ugly to live on, etc.
- Old players after loosing their characters or getting tired of the game are willing to rejoin with world reset to see all the new content.
- A nice marketing message of the new server opening: creates the feeling of a race, competition for those who start new game.
While older world becomes less and less attractive and more and more unsafe place, where only most dedicated factions with lots of time and AI rule the lands - the game becomes less attractive to return or to start a new adventure in it.
In conclusion, I'd suggest opening a new server (world) every N month, not necessarily killing the previous one. This is something what Salem tried to do, but failed initially. That'd be healthy for the game if done right.