You can prevent it by just creating a good mod where people want to leave NW for.
Sorry B&I and other mods your quality in gameplay and the overall modding standards are just low and that's the problem.
Not releasing or later releasing the server files will not help and will only annoy the fair users.
I would say, that B&I, NaS and BC are modded very well, with some nice gameplay (thats why NaS is still played by hundrets in line battles).
When we released the server files for BC, we had
50!!! running servers. Nearly each legion had its own server with some tiny amount of player. To avoid that, its better to have 1 central server.. to get public play successfull!
That move of releasing public server files destroyed the whole mod..