I'm reasonably worried that, if 2Dev manages to finish up collecting the badges and medals, he will disappear suddenly and we will never see him again, just like every other good player that's come before him. (Not that anyone's ever gotten ALL of them, but it's related to that.) With any luck, 0.9.9.7 will have a lot more "to do" for a collector, and it'd be a shame if he left before that happened.
I doubt that the good players of the past left because they ran out of things to do in the game. Sometimes, real life just takes precedence over gaming. DoomRL is a great game, a very fun and addictive game, and I heartily commend Kornel for his work, but in the end, it's just a game. Diversions like this come and go and it doesn't indicate any fault in the game or in the people playing it if those people decide to find something else to do. And no game, no matter how good, can take more importance than, say, having a source of income and having social interactions with family and friends.
Speaking for myself, my periods of playing the game correspond most heavily with periods when I was most depressed. I first discovered the game in late 2010 after losing my job, then stopped in April 2011 when significant positive developments occurred in my social life, then started again in late July 2011, when everything went wrong again. DoomRL helps fill a void in my life by distracting me from my real life problems, so I guess you could say it's some weird form of therapy. :) (Although, it's probably not the "healthiest" coping mechanism out there) My point is that the period when I stopped had nothing to do with the game itself and if I stop playing again, it probably won't have anything to do with the game then either. I can't speak for 2Deviationsout in terms of what motivates him, but I'm guessing that, as he said, he won't stop playing just because he gets all the medals. There will always be another seemingly unbeatable goal out there... even if it's Angel of Pacifism Conqueror. :P
Erm... sorry for filling this thread with philosophical ramblings about gaming. I'll try to karmatically balance this post by donating. Now that I have a source of income again, it's about time! :D