If you want to keep this community alive, I think the only ways would be:
1. move to vengeance (by using someone else's mod, if there is one yet, until you finish one of your own)
2. Make some really good changes/updates to the mod. You would definately have to redo the inventory code (for more items), and change the zones alot or make a completely new map)
3. Move to a new game completely. You could move to an MMORPG if you wanted the community style to change (wouldn't be Partiicle's Custom anymore). No matter where you go it will start slow, since there are so many people playing the new games..
You could advertise in other servers (non-RPG mods), but you'd have to stay un-intrusive about it.. there aren't very many other people to advertise to though. There are only like 125 servers up now, and 85% of them are empty all the time.. I think your best bet is to move to another game.