He doesn't owe any funds to the campaign participants because it is not his fault since they didn't come online and no other communication that forum account.

But my humble suggestion for any campaign managers while self escrowing a campaign will be, put you campaign paused when you doesn't have enough funds to pay the participants for the next coming week so participants were aware of the situation and let the participants to wore signature on their own risk.

I often see this kind of announcement from yahoo when he doesn't get top-up for ongoing or next weeks.