I mean yes anything can happen as planesandthings said. We're living in a world where nothing is certain anymore.
I doubt though there would be another recession so soon, banks have made sure that won't happen (hence the difficulty in taking loans), and also if you read up a bit about the airline industry, its at its strongest its probably ever been (warren buffet has just invested billions into airline stocks). Airlines are more careful now with over capacity and with handling crises.
Another 9/11? Highly unlikely. Though 2015,2016 saw the shooting down of a malaysian airlines flight over russia, the mysterious dissapearance of MH17, a suicide air crash into the alps and a few other note worthy crashes (flydubai,air egypt etc)...yet here we are, and they barely affected the industry. The truth is the industry is more cautious now and certain events are protected against. Many airlines have consolidated and have become more robust.
It is more likely the airline you might join is to go bankrupt due to misaporopiate handling rather than other external factors...though airlines like EasyJet are known to plan ahead, hence applying for an EU AOC years before they even know the impact of Brexit (which could be years away)