We’ve had MMORPGs (massively multi-player online roleplaying games) for a while and now we’re increasingly just calling them MORPGs (Multi-player online roleplaying games).
During a conversation with friends we decided you needed Smallish-Multiplayer Online Roleplaying games (SMORG) to cover old games which have shrinking player bases, games which never really took off, and games which naturally thrive with small groups of players.
So, feel free to use this term.