The cooling of speculation in the oil market is almost certain to help Norwegian get through the summer and, I suspect, the fall. Fuel is a huge expense for them, and a 15 cent decline in jet fuel prices (which we've seen in the past week) is a big deal for a struggling transatlantic airline. I also suspect the huge demand for summer transatlantic travel will result in more "spillage," as budget conscious consumers will balk at sky-high "last minute" fares from the "full service" carriers.
Norwegian's real problem is the non-peak transatlantic season, which I'd say is about 8 months of the year. There's more supply than demand for coach seats during that time, and the big boys make their money (to the extent they make money) on premium cabin travellers after the summer leisure rush. Coach seats sell cheap during this time period. I just bought seats on DL to Spain for $250 roundtrip for April yesterday. UA, AA and Iberia had similar fares, and it's pretty easy to buy such seats under $400 to most of Europe in winter. This is the fundamental flaw in Norwegian's business model that won't be going away.