Right now, when a players finances detoriate and he does not declare bankruptcy, the planes continue flying but the maintenance is not made anymore. While the company gets penalties for that, they don't hit him anymore if he is circling the drain anyway.
Along with the players finances, his planes condition will also detoriate. So much that eventually, when the bank closes him, the AI brokers will scrap a boatload of planes, no matter how attractive they are to the market.
Take for example CS Global Airways in MT9:http://www.airwaysim.com/game/Info/Airline/View/218/133/#AirlineInfo
He has been beyond repair for several months now but does not close his shop. Already many of his planes will have catastrophic condition. The longer he draws this out, the more planes will be trash before the bank will eventually close him down.
Among them are also several planes very attractive to other players and a noticeable share of those will be scrapped when he collapses.
So, long story short, I propose that brokers auto retract their aircraft if they drop under, say 30-40% condition, to prevent scrapping (I have no idea what level of condition is required for them to be auto-scrapped, so the number is pretty random). This way the planes could be saved and wouldn't be lost to the other players.
I saw this happening multiple times last MT and it's about to happen with multiple airlines again now.