Since I have been gaming for over 20 years, I am only going to go as far back as the longest running player in my current group.
In September of 1999, I had DM'ed a grand total of 2 sessions of D&D since 1992. One of those two sessions, this one in August 1999, was with some former students who had graduated previously. I had recently moved about two hours north. My wife went to Buffalo, NY with her mother for the wedding of one of the members of our bridal party, but I had to work, so I stayed home. While she was away, we were visited by Hurricane Floyd. I was home alone with no electricity and no work for about a week, so I took to hanging out at a FLGS. The owner asked me to DM a weekly game in his store and he advertised for players. Seventeen of them showed up for the first session. One of those was the former student I had recently gamed with. He had also moved to attend college nearby. The group took some time to stabilize, but we had the same core group there for over a year, including one player from my high school gaming group.
The following summer, the player from my high school gaming group married another current player and they moved away. Most of those players drifted away, except two, one of whom is still gaming with me. The former student gamed with me until this past winter.
Another of my former students has been in and out of my group since 2003. The one player from my FLGS days that is still with me brought his best friend to the game in 2003. He had been at my original FLGS session, but left because there were too many people. He is also still with me. Two other players from the FLGS group just recently left my group.
The rest of my current group came from another local group. I met one of their members on a message board online (though not ENWorld) and he joined my group and eventually brought the rest of his group to mine. The final remaining member of his group is joining my game next week. He is moving away after next week's session, as is the former student, who is joining the US Army to be a combat medic.
It appears thatg the second group is going to entirely fold into mine (which could necessitate the rotating DM's I have been asking about) due to players leaving the area. My group has had to absorb the other to survive for the same reason (as well as my well documented player troubles).
DM