I think it was more a case of IAG not wanting to buy, than NAS not wanting to sell.
That is a glib unsubstantiated statement that is at odds with all the known facts. IAG bought almost 5% of NAS at a cost of many tens of millions, a stake that it still owns (after all the due dilligence). Willie Walsh has stated many times that is remains interested in buying Norwegian. We know that two offers have been made for a price well above the current market cap. I addition another expression of interest was made by LH.
Norwegian has always been ambitious and has sailed close to the wind. A spate of technical problems with RR engines, an unfortunate diversion to Iran and the recent Gatwick drone woes have not helped. However Norwegian has a good product that consumers love, it owns a significant amount of assets and its partly owned by the biggest sovereign wealth fund in the world. Norway itself relies on Norwegian to connect a dispersed population over a large country, it won't let it go bust over some short term cash flow problems. If it needs a bit of breathing room I am sure it will get it from current and , if required, outside investors. Taking a breather from breakneck expansion is a good thing and will only make them stronger for the future.