Any external (Russian) pressure or attack on NATO would have strengthened the alliance. Same would be the case for problems in Germany, whether they were entirely internal or inspired from Moscow.
After all, the whole point of the alliance was "to keep the Americans in, the Russians out, and the Germans down"
Dissolution of NATO would have to come from within NATO. In particular, most probably the UK would have to lead the effort to end the alliance.
So, if I were to write a novel that included the dissolution of NATO, I would describe a radical socialist/communist rise to power in London, which in the initial phases would have to be through the electoral process. Given the economic and social conditions in the major cities of the UK in the years following the end of WWII, the rise of the radical left would not have been impossible.