The key areas affected are the travel and hospitality industries. Airlines, hotels, restaurants, car hire etc. Without help they will be demolished and could never return. Aviation is so expensive (not least because of insane taxes) and competitive, and margins so tight, that airlines pay current costs from the cash flow generated from future ticket sales. Once those sales stop, the airline goes under.
That's what happened after 9/11. Many smaller airlines without government assistance went bust.
Most airlines already have plans to lay off much of their workforce. Delta in the US has already cut 40% of flights and staff layoffs will follow.