Many struggling (high cost) airlines have implemented the ability to sell seats on the airlines of their partners.  It's called "code sharing" and is a survival tactic.  I don't know of many mergers or buy-outs that resulted in lower prices or better service but that's what is claimed will happen by the proponents.

The benefit to the customer is a "seamless travel experience" with through ticketing, luggage, frequent flyer earning and spending ability and more.  While claiming that prices will not go up and service will not go down, the airlines say it will allow them to get more revenue.  I don't see how all of this is possible at the same time.

Nevertheless, I'm not worried because nature abhors a vacuum.  There are hundreds of fairly new (or brand new) passenger jets parked in the desert, there are thousands of very well qualified flight crew available and there are lots of available gates at airports.  The high cost airlines can not afford to fight a multi front war.  They know that if they raise prices or cut back on service, a low cost airline will enter the market even faster than is already planned.  The code share arrangements insure the short term survival of high cost airlines yet do not give any assurance in the long term.

Until the high cost airlines significantly reduce their labor cost, increase the flexibility of crew, fleet and flight options while moving the employee attitude needle to the positive side, their fate is sealed.  Even if they do not file chapter 11 or chapter 7, they will shrink to a size that will make them a niche or regional player.  Without these changes, their only other option is to turn over as much of their route network as possible to their commuter partners with their regional jets.