That's not much of a problem since they can just modify the airports like they did for the A380. (Not that airplanes need to keep getting bigger for Airbus/Boeing to keep selling planes.) However, if no one flies in 100 years (transporters, etc), then it is unlikely Boeing or Airbus will still exist. Technically Airbus isn't a company anyway, it is part of EADS.
Something tells me that Wal-Mart, Coke, and Southwest Airlines will still be around in some form or other. As for companies that will be gone, I think the tobacco companies are at the top of the list
I think that when 3D printers become cheape, quicker and easier to use there wil be companies that will either go out of business, or suffer greatly, similar to the way Kodak was affected by the move to digital cameras. I wonder if Lego or Mattel etc are concerned about 3D printers?
You will not be able to print a Lego brick without having to pay for it. Besides that, just printing something isn't enough.
Howard Johnson's restaurants are pretty much gone. The motels are still around. Pan Am would probably still be around if airline deregulation hadn't happened. (So would National, Braniff, Eastern...). I'm sure Apple and IBM will be around forever. Like cockroaches.
But you will be able to design your own bricks that is either compatible with Lego or is a standalone brick building system.
People are also able to produce their own films today. That doesn't have an effect on the incomes of professional films (the digital distribution channels and piracy do). And you're not going to do your own film if you want to see one, you buy the final product because it takes less effort to make. That's the way I see it. The majority of people is not going to produce its own Lego kits because it's a lot more complicated. And pirating existing LEGO kits will be quite complicated as well. When stuff comes out of a 3D printer, it's still pretty raw and needs further processing. And that won't change. It's comparable to printing your own photographs or burning your own CDs and printing your own CD booklets. You have a hard time matching the quality of professionally produced items.
I'd guess the companies that have a wide variety of different products would be the ones most likely to survive, like Honda, not the ones that focus on a single product or service industry. Not only that, but the final costs will likely still be too great for an individual. The larger companies can make things cheaper for the consumer by making their products in bulk. An individual won't be able to do that cheaply. But, I would bet on creating personalized or unique LEGO-compatible bricks!
Wal-Mart makes it until at least the late 24th century, because they bought out Weyland-Yutani in Alien: Resurrection.
The companies still around will be those who had the sense to diversify and aren't reliant on the fortunes of a single industry or commercial activity. Virgin, as a well known example. Those dependent on the pre digital way of life (especially physical media) will fade slowly over the next few decades, including I suspect some really big names.