Norway itself eventually fell under Nazi control, but Narvik especially suffered. The end of the movie explains that the town was bombed by German planes after the British and French left. Everything from buildings to streets to ports got utterly destroyed by the bombardment, but that didn’t stop the people of Narvik from rebuilding after the war (per Britannica) had finished.
The entire process of invasion, fighting, victory, and destruction played out over the course of just two months. The Nazis claimed the town on April 9, just as the British were preparing to lay bombs all around the port. The sea battle was easily won by the British, and five days after the fighting began Allied troops joined the Norwegian forces on the ground. The battle lasted over a month. It wasn’t until May 27 that the German soldiers were defeated and Narvik was reclaimed by Norway.
Sadly, Narvik didn’t hold out much longer after the victory, and neither did Norway itself. On June 7, according to Britannica, the Allied troops left for France, and the king of Norway left his country for Londo. Just three days later the Nazis took control of the entire country, and Narvik was destroyed.