If the person who asked the next question, PMed a moderator the answer to the question. Then if the member that asked the question was offline when it was answered, the mod would know the correct answer.
(example: I asked a question, then I PM Nifty (or another mod) and tell him the answer along with the question. If I end up logging off, Nifty (or another mod) would have the correct answer.
The members could just have a vote and if a certain amount of people agree that it is the right answer, a new question is posted. (Like us 3 just did)