WI: (North) Yemen remains a monarchy?

From The Middle East Today (1994), pp. 486-487:
Unrest among Zaidi officers who wanted to modernize the armed forces, backed by sophisticated Shafi merchants, culminated in a plot to overthrow the monarchy in September 1962. Led by Army Chief of Staff Abdullah Sallal, a five-man revolutionary council was established to form a republic "based on social justice."

At the time of the revolution, the new imam, who had ascended the throne only a week earlier, was presumed to have been killed. However, the imam and others in his family escaped, to lead a tribal force of loyal Zaidi followers against the new republic.

With support and assistance from the UAR, President Sallal proceeded to organize his revolutionary government in areas, mostly urban, under his control.
What would happen if this was somehow averted or simply thwarted? I do know that UAR troop presence in the subsequent civil war had an impact on the rebellions in South Yemen (then a British colony) as well.
 
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