The Hungarians in '56 and the Czech's in '68 revolted against Soviet hegemony. The Czech's helped put down the Hungarian uprising, and the Hungarians helped put down the Czech uprising (among troops from other Warsaw Pact nations). Soviet troops were generally stationed in Warsaw Pact nations helping to ensure local cooperation with the Soviets.

Since the Warsaw Pact was never directly attacked by the West, it is impossible to determine if the Pact would have held, however, I suspect it would have since the Pact maintained the status quo against "internal" rebellion.

In both the Hungarian and Czech uprisings/revolutions/springs (whatever you want to call them), the West sent messages via the radio that they would support the uprisings - and then they didn't. That hurt the West's credibility and indirectly strengthened local solidarity with the Soviets (no pun intended with for the Solidarity movement in Poland in the 1980s).

I don't have the background to address the issue of a potential war, but the Soviets certainly used many things to nurture the loyalty of countries within its sphere of influence. One of them has had a long-term impact on the economy within many former Soviet client states, even decades after the Soviet Union's collapse.

Under the guidelines of most Soviet/client state treaties (and often, though not always, within the context of Comecon), countries were allowed to purchase major commodities at a fraction of their actual value on the international market. This was referred to as the "friendship price." For countries within the Warsaw Pact and non-WP states like North Korea and Cuba, that meant getting things like oil and gas (or anything else that they couldn't make for themselves) at around 25% of what they would have paid otherwise. The "friendship price" was at least nominally about the more-fortunate states within the Soviet Union helping the less-fortunate, but for any nation that didn't have the hard currency or resources to pay for commodities on the world market without it, it also meant severe economic dependency on the Soviets.

As you'd expect, the economies that developed with the use of the "friendship price" had severe shocks when the Soviet Union started to collapse and renegotiated the terms of, or simply ended, the friendship treaties. The former Warsaw Pact countries have (with the exception of Albania, which is still working toward more stability) reintegrated with Europe and are working their way to parity with their western counterparts. However, for countries elsewhere, and particularly North Korea, which was never really viable as anything other than an economic dependent of the Soviets', there's been no true recovery.

I'd just like to point out that your comment reads to me as implicitly supposing a sort of unity and stability on the part of American-allied countries that seems questionable to me. In Africa, Asia, and Latin America, such governments were fairly often the targets of popular uprisings, and the existing governments, the United States, and the old European colonial powers demonstrated that they weren't shy about using force to maintain the existence of allies.

In the NATO countries and the rest of Western Europe, there weren't any successful socialist revolutions, but there were definitely sympathetic mass movements, and the governments of those countries definitely feared the possibility that Communism might take root among the populace and were willing to use force to prevent it. See, for example, Propaganda Due in Italy.