In 1953 Stalin would be too cautious to launch WWIII on purpose. However his mental state was deteriorating, and thus it's possible that he could eventually reach a state where either he decides that war would be a good idea, or he does something so stupid that it makes WWIII inevitable. I'm not saying that's going to happen, but it's a possibility.
There is Yugoslavia, Stalin had plan to invade them as he can't stand anyone not in his control, but OTL the Korea prevented this...maybe if the war in asia end like OTL he can decide to recoup there (probably due to a failing mental health...thing very very possible after a stroke, there are many cases of subtle or not so subtle change of personality that can be associated at the damage received.)
In any case in the 50's there are been a lot of crisis that can easily escalate:
- Vietnam (more tension can bring the US president to greenlight operation Vulture)
- The First Taiwan strait crisis.
- The Syrian Crisis of 1957
- Suez in 1956
Just to make some example
There was talk of using nukes if the peace talks failed....(although it's hard to say if the US would have gone through with it).
The US reaction/the Red Scare will be the subject of another update. For now suffice to say that it's going to be worse than IOTL.
Oh joy, McCarty for president
The true believer Communists will for the most part continue to believe, since after 20-30 years of singing Stalin's praises its psychologically easier to think he's a good guy then to admit you were duped for decades (and other factors like a natural distrust of anything the US says about the USSR).
While true believer will not be swayed at this stage of their lifes; this are no more the 30's with the 'ism' on the rise due to the perceived failure of previous structure, or a population spoiled by the war propaganda being much more suspicious of big claim than before (see Rape of Belgium).
Speaking from an european pow, this can bring a rise on the number of social-democrat and socialist and an serious hit for the communist parties, and in any case after the old leadership has been removed a much less dependence on Moscow in leadership.