A Mere Suggestion...
 

I don't know if this has come up before, but how about flags and variables that can travel from one server to another? My idea is something like: Maybe on one server there is a quest for an NPCW, and once you get it, it sets some flag. Then when you go to some other server, the flag goes with you and you are able to have that NPCW (if it's been scripted on that server). Thanx for reading.

flags and strings stick to the player-follow them in any level
variables stick to the room-reset when the room's empty
this.variables stick to the NPC-reset when the room's empty, follow the player if it's an NPCW, and reset when the player relogs
save variables are weird, they're supposed to store the value until the level's reset but they've given me nothing but trouble. I use hearts, rupees, ap, bombs, darts, and the like when I want an NPC to keep track of something.
server strings apply to everyone in every level on the server.
Apparently with NPCServ there are server variables too, or something.....