Majog, the team concept that Earl uses for these games helps greatly with the disappearing player syndrome.  First, I think people are less likely to bail on a team anyway, but you also have built-in backups.  If a team has a player that needs to drop out, Earl will usually try to find a replacement.
Regarding disappearing opponents players in general, check out Rule of Engagement #9 in the club rules (available from the navigation bar at the top of the page).  It states that any documented case of an opponent disappearing for more than 3 weeks means an automatic Maximum Victory for the remaining player.  That's been there for a long time now.
Earl, you put a ton of time into these campaign games, and deserve a huge amount of credit for dedicating so much on helping other people enjoy the CS series in a whole new way.