Given that quite a few of the top US airlines are already operating in Bankruptcy, including United and USAir, I am not worried about holding tickets with Delta. In fact I have two Delta (Song) itineraries booked currently (April & October) and will be booking another later this month (for February '06). The one to worry about is USAir IMO, tho they do seem to keep on flying anyway, despite their apparently hopeless financial predicament. United is having trouble getting back out of bankruptcy, but I think we all expect them to keep on going. Delta is still a few notches up, and using the threat of bankruptcy as a means of winning concessions from bondholders and other creditors and from employees.
Just to restate, we Delta ticketholders will be just fine. In fact, we should benefit by their efficiency initiatives and the simplification of fares.
Don't worry! They will get us all there.