Debt is mostly in plane leases and quite a bit to of US export finance who will not be interested in owning a foreign airline. All those planes sold at overprice on delivery against a overcost leaseback would have to have their leases renegotiated or planes returned. Preferably by a company that have other business with the same planeowners. Or a cash rich finance company with an interest in the airline industry that could buy out the planeowners at a discount in the current market and lease the planes effectively back to itself. And then in 3-5 years, when Boeing the Max payout has been scooped up and markets normalise, relaunch Norwegian back to the market as a well financed and well established airline. I could se a 5 to 10 fold payback on initial investment.
Pricing of a takeover would need to be in the 1-10c a share range through an enormous expansion of number of shares, to which existing shareholders for legal reasons would have to be invited to participate. Any pure buyout of existing shares would just be giving money to existing shareholders and would not only increase the price but would neither help the company survive. A new top management team with extensive airline experience and preferably scandi experience would also have to be put in place.
An umbrella company like IAG could be an option, but I suspect they don't want a long haul low fares competitor to BA or a Spain competitor to Iberia, so would shrink Norwegian to Scandinavia only taking away halve the advantages, but there are others.