If this submarine had got lost when the Falklands war was a hot war, would the British lend them a helicopter or two to help them look? Particularly if it was a day or two after the Argentine Air Force had taken out a ship or two of the Task Force.
'Here you go guys, if you need help with salvage...' would not have happened then or in the post-war aftermath. Instead the Royal Navy would have denied the Argentine armed forces access to the area and the depth charges would have been deployed, the submarine gone for good like the General Belgrano. The victory would be selling newspapers. Only a few left wing anti-war moaners would be grumbling.
But today obviously there is 'peace' and as much help as much as possible is coming from the British establishment with no hesitation.
If the North Koreans lost a submarine would other countries such as the UK/USA offer them help to find it, particularly if it could one day point missiles at the USA? Maybe there should be an on-going 'lost-submarine test' where world tensions and hostilities are gauged by how many countries participate in military search and rescue operations.