But the campaign does continue. From the viewpoint of the game, that's what matters.
Example: I was in a 3e campaign from its founding in 2001 until I dropped out sometime in 2007. That campaign most certainly did not end at that point and in fact will hit its ten-year anniversary in a few months...and it's still relevant to me as well; though I don't play in it I hear the "media coverage" of what happens from those who do, that campaign is included in our annual awards, and so on.
[MENTION=18280]Raven Crowking[/MENTION] - that business with your LA campaign continuing after you left is just amazing!
Lanefan
Sure, others may continue playing in the campaign, but it is over and complete so far as those who left. Sort of a relative viewpoint thing.
Let's assume RC decided to continue his campaign once he reached his new city. Two years later he hears that his old group continued the campaign. But that can't be right can it? The campaigns almost certainly went in different directions with different DMs, different notes, and different players. How could both claim to be continuing the same campaign? Relative viewpoint.
RC can claim to continue the campaign because he was involved and is running the same setting with the same history with new PCs.
The old group can claim to continue because they were involved and are running a similar setting with the same known history with original PCs.
If I have a favourite character that I run in campaign A and then I leave campaign, the fate of the character after I leave is not meaningful to me. If campaign B picks up and allows me to bring in my character, I'll bring it in as it was when I last played it regardless of what may have happened in campaign A. To me, the campaign existed only so long as my involvement. It may have existed prior and it may exist after for others, but it didn't impinge my life save for when I was involved.
The DM have no authority other than to direct his own time and accept/limit the involvement of others with that time. If he offers to run a particular campaign, that's nice and all, but the group and the individual players must decide if to participate.