Every member of the co-op has some response time obligation: we will feel free to let members' services stop working if they don't respond to e-mail after, say, a month, and we will feel free to kick members out of the co-op after the time period of non-payment specified in our HcoopBylaws, sending warnings only through e-mail.
However, members who volunteer for particular roles take on additional, far greater communication responsibilities. One volunteer in a key role can derail our entire operation by not communicating effectively.