In most reservation systems, flights will drop out of availability after (or even slightly before) scheduled departure time. Some systems have a way around this manually (long selling) which bypasses the availability display entirely. This is a pretty narrow corner case which may not be worth the time for JetBlue's system to address (or worth the staff's time in Austin). What about buying a ticket on a later flight and standing by for this delayed flight? The departure control part of the system shouldn't have any issue adding passengers to a delayed flight as long as they already have a ticketed reservation. I suppose you could also try sending them a message and see what they say.