Hmm, either leaving makes the server crash or the multiplayer is still so basic that if anyone leaves, the server quits as well (i noticed all singleplayer aspects still work the same way in multiplayer)
It didn't crash right away though. What's interesting is that when the server crashes, instead of booting you out of the game, it transitions in to a singleplayer mode.
Actually, the developer is doing work and has been updating his twitter daily. I'd imagine at least a month til an update, but dead game is no longer dead.