Expedia and Booking have been around nearly 25 years and both have well over 20k employees. Seems like travel has more than enough margins to support multiple companies that size.
Yes, everyone fully understands with travel at a complete standstill, none of these companies are viable if the current situation were the norm.
But the current situation is not the norm, people will eventually get back to travelling a lot, and when they do there will be plenty of economic activity to support large companies in the travel business.
An extended shutdown with shut borders may have long-term effects on consumer's willingness and desire to travel. If the travel industry remains shut down for the next 12 months it's not unreasonable to think that the travel industry wouldn't fully recover for 10 years.
Or maybe pent up demand will have the opposite effect. There's no way to know.
I've had the same thoughts about the restaurant industry. Will lockdowns create a generation of home cooks, or will be so tired of staying in that the restaurant industry booms after this is over?
9/11 had a similarly chilling impact that shook the airline industry to it's core. Covid is likely going to be worse for the industry than that, but it's not without precedent