It would be difficult to implement realistic mergers and acquisitions (M&A) into AE.
First, the "sales price" of an airline would be its enterprise value (EV).
EV= Market Cap + Debt - Cash
Without a stock market, you can not figure out market cap (market cap = outstanding shares*market value of shares)
Even if we used an airline's valuation as a stand-in for market cap, we can be stuck with people creating ghost airlines to run up debt and then purchase with their main airlines.
But then we must look at the benefits of purchasing an airline. These include:
All existing assets (terminals + owned aircraft)
Rights to any aircraft leases
Rights to all gate leases (especially those hard to get foreign gates)
Rights to all existing routes
And we also have to look at legit reasons an AE player would want to sell their airline. Some reasons are:
Excessive competition
Excessive Real Life demands
Having other better ranked AE airlines they'd rather focus on.
So there are legit reasons to have M&A
One way that this can be implemented is that only airlines with positive valuations can be sold.
M&A can only be done after an arbitrary amount of AE round years
Only airlines who put themselves up for sale or airlines with positive valuation who are inactive can be part of M&A
Once that airline (Airline A) is put up for sale, that player loses control of their airline
"Airline A" is then announced to be on sale for anyone in the same home country to bid for
Once the bidding window closes, the winner (Airline B ) is announced.
A month or so later, all assets, leases, routes, debts are transferred to the winning airline (Airline B )
If Airline B pays more than what Airline A is worth, that difference shows up as "Goodwill" on the balance sheet
No airline receives the proceeds from the sale.
What are the downsides of M&A?
Decreased employee moral. There will most likely be differences in pay between Airline A & B which will cause an uproar when Airline A's employees get pair more/less then they used to. Also to achieve synergies, redundant positions will be reduced during the first year of merger causing a reduction in employee moral.
Increased payroll. Until synergies are achieved via layoffs, Payroll consists of total payroll of A&B
One-time training costs. Employees of Airline A must learn the best practices of Airline B
Rebranding cost. Painting aircraft, changing logos at airports, new uniforms etc. (just like if you changed your airline's name in game)
Reduced reputation based on the difference between airline's reputations
More advantages?
"Merged" aircraft deliveries. Take over delivery spots of Airline A. You can now receive 2 737s every 2 weeks until Airline A's queue is finished
plus all previously mentioned
Airlines with negative valuations would not go through this process. Without a solid bankruptcy protection program in AE, leasers will repossess all aircraft and placed in used market, airports will remove unpaid gates and place on the market, and airline would be closed as is done currently.
[sorry, I'm bored]