Gromgor, your question about airlines has been answered by multiple people. If you don't like related side-tangents, then don't participate. Quoting someone's entire post just to say it isn't talking about airlines is just spam.

Airlines are more important to the country as a whole than most small businesses. That is just a fact. The government coddles them because the economic impact of not doing so would be enormously negative. If Mom-and-Pop's neighborhood shop goes tits up, the overall effect on the economy is negligible. That doesn't mean there is no effect, there just is not a big enough effect for it to require government assistance.

It is an economic disaster for even a single airlines to cancel flights for a single day. Too many businesses depend on their employees being able to travel via air or for tourists to travel to their location via air.

That along with the power of unions (who don't want a union airlines replaced by a non-union one) means it is almost impossible for an airlines to actually close up shop.

That said, it is still important to note that almost any business can file for Chapter 11 bankruptcy protection. This is known as "Corporate Reorganization." Chapter 11 gives a business more time to pay its debts while continuing to operate (and bring in money). Many businesses, even small ones, make use of Chapter 11.