NATO has generally been a force for good and why would Uk withdraw, the French did under de Gaulle but there was never the least doubt which side they were on. Simialrly Sweden was neutral and not in Nato and it was just a coincidence that all their equipment was NATO compatible.
The real danger to NATO is America or to be precise a loony right wing America under the likes of Trump why might break it up by accident although i am sure other US Govt forces might just think that too much for them.
The other tricky bit is that the US -UK relationship which smoothed a lot of transatlantic conflicting views over might weaken since the US cousins like dealign with the people who really matter in these affairs and these days thats Hollande and Merkel who can intermingleNATO and EU politics leaving us as sort of nuclear armed Billy no mates -an odd situation