If all other party members are in town, in another zone, or dead during an event OR boss battle (one that awards a "cooperative achievement"), will the event/boss battle still award the coop achievement for the whole party?
For example, the other party member in a two-person party stays in town during [an event]—does he still get the achievement, and do both get the cooperative achievement even though the other party member wasn't present? Or everyone declines a boss battle while one person finishes it—do all party members get the achievement AND the coop achievement?