Just because a lease was signed x years ago for aircraft, doesn't mean that when it comes up for renewal the price will be the same. Its a marketplace, prices are negiotable. I would not think there would be a bidding war on a dozen 15yr old J41's. If eastern handed them back they would probably be parked up and left to rot.
Logically the 41 fleet will be replaced, when they get too expensive to run, and a similar replacement becomes available. I don't see that happening anytime soon. What other 30 seat turboprop is still in current or very recent production? They may aquire a few more saab's who knows?
The signs of an airline in financial trouble are usually mass cancellations , crew not being paid , difficulty obtaining fuel and handling, broken down aircraft not being fixed etc. There is no sign of this happening with eastern as far as I can see.