"The industry will have to evolve before we get another round of mergers," said Joe Schwieterman, a transportation expert at DePaul University. "We could see one of the niche players be bought by one of these large airlines, but I don't think any of these four will be able to combine. I think we've reached the finish line."

And while many believe American had to make this deal in order to compete with its larger rivals, being the biggest doesn't assure it of success in the market, said airline consultant Mike Boyd.

"Being bigger doesn't make you more powerful. Ask any brontosaurus," said Boyd.