Etiquette around a GM ghosting a game
If you're setting up your own version of the game, you should check the flags on it first...I believe (but could be mistaken...if I am, someone will correct my error, I'm sure) that if the 'sole ownership' flag is set, you're not allowed to copy anything from that game to create your own version of it (at the very least, it wouldn't exactly be kosher to do so.)
That said, the longest-running game I've ever been in on RPOL (and it's getting close to have the title for anywhere, just another year or two and it will beat the decade-and-change Star Wars campaign I was in through college and into life afterwards) started because our GM vanished and one of the other players decided to start his own game. It wasn't the same...or even similar at all, really, aside from being a game about Earth fighting against hostile aliens, but it was set in a different century, with different technology, and different aliens...pretty much everything except that central theme was different. But within a couple of weeks of those of us who were still active coming to a consensus that we'd been abandoned by the GM, he posted about his game and invited any of us who were interested to join up.
The etiquette regarding that depends largely on the individual GM. This guy has not only advertised for his other games in that game, he's allowed any of his players to make pitches for their own games or games in which they participate. I know some GMs are extremely averse to anyone advertising anything in their game, but at this point, it sounds like he's been derelict in his duty as GM and it's fair game to promote whatever option you want. You can, for good measure, say that you're only doing it because you're pretty sure the game is dead, but if it starts back up, everyone is welcome to play there as well as in your game (just to clarify that you're not trying to steal away players, just offer them an option to fill up the unexpected free time they now have because their GM has gone AWOL...it's not demanded, or even expected, necessarily...but it's still a good gesture to make.)
And, like NowhereMan, I've had GMs return from lengthy, unannounced absences and resume games where they left off...I had a Shadowrun game that had been dormant for so long that I'd removed it from my sticky list and figured it would just vanish in the breeze at some point, and then one day about a year and a half after my last post in the game, I got a PM the GM asking if I was interested in resuming play. Never did find out the reason for the extended absence, or why it came up so abruptly. Life happens...I was just glad to have a fun GM back.