The EU MGO clan (Wasp Unit) outlived the others because of superior leadership and a core handful of dedicated Gaffers that ended up as friends. There was about 8 of us that played regularly. Everyone else, like you say, disappeared for other games or better things. Console online gaming moves a lot faster than PC, unfortunately.
They were some brilliant months, we were inches away from becoming EU champions in the tournament, and that's where that all ended. Felt too much like work to get to where we were and we burnt out.
Similarly with Killzone 2. The EU gaf clan filled up hardcore, but so many people just signed up because it was 'TEH GAF CLANZ.'
We're left with a solid core of around 16 or so guys now, i'm glad to say a decent chunk of my brothers from the MGO Wasp Unit were there, even if they aren't playing anymore. I haven't really played much recently, but we have the GAFe chatroom running and everybody idles in it, irregardless of what games people are playing. Glad for my time with the Hero Kings and Queen of GAFe, all solid, decent and gorgeous people. Even FFO in his brown coat (i haven't seen it ;p).