There was some discussion in global today about co-op addies. Apart from the loot issue (having been made considerable less attractive in the big loot nerfvember overhaul) the biggest problem with them is the player who goes awol and holds the other players up indefinitely.
Is it possible to measure player activity in an adventure zone?
If so I suggest that after an hour of inactivity the host of the adventure has the option to boot the awol player from the adventure and send out a new invitation for the remaining camps of that players sector. The booted player will get rewards as per a cancelled or timed out adventure.
As someone who has been stuck for several hours by an absent player on a coop, I'd be much less hesitant to start one with players outside of my guild if I knew there was some safeguarding controls for that scenario.