trouble is Norwegian own quite a few of their 788 and 789, thus they have to find a leasing company to buy them (presumably at an on paper loss) who will then lease them on to another airline. Some are still undergoing engine rectification as well I believe. I would have thought they'll be picked up by an airline looking to downsize 777 or similar since they are nice fairly new aircraft, but wouldn't see it as a short term risk for Jet2.
Having said that, pre-pandemic, they chose to take the ex Thomas Cook A321 aircraft primarily because they were available at the right price, since it was a significant move away from their otherwise B737-800 fleet....