Things I beg for the developers to do or give us the option is an endless world with no time limit.
My suggestions......
1. You can't quit and if you do then your Airline is offered on some kind of market based system where the highest bidder can buy it, and which then will transfer all routes and airlines to the buyer company.
2. Stock system.
3. The ability for airlines to loan each other with interest.
4. The ability for another company to buy certain stakes of your routes.
If the developers can achieve this then this will be the best Airline management game on earath,