The idea that the industry, Jet2 included, won't contract between by 10-20% as so many holidaying people have lost jobs is difficult to argue against now, since the 23rd March a lot has changed.
True, but this isn't a "normal" financial crisis. A lot of those 10-20% haven't necessarily lost their jobs permanently but have instead been temporarily layed off. It's possible that the economy will rebound a lot quicker compared to previous examples. In an optimistic scenario we get on top of coronavirus over the next few months and life slowly returns to normal. This summer is clearly a write-off for most airlines but I don't think it's inconceivable that by next summer traffic is back close to February 2020 levels. Certainly the 3+ year depression people on these forums seem to be assuming is by no means guaranteed.