I can't help but to think that when the revolution occurs, what will stop the people leading it from becoming the tyrants de jour? There is no reason for the new leaders to surrender the power back to the people that so empowered them.This is a good question. Obviously, there are no guarantees: you pays your money and you takes your chances.
But there are some reasons why it's in the best interests of the revolutionary power to forswear tyranny and work to the benefit of the people. Tyranny by brute force, in opposition to the social and psychological structures in the masses are very unstable. Brute force tyranny is most often seen in imperial domination, and usually requires massive support from the dominating imperial power. A "successful" tyranny requires some level of socially constructed consent of the masses.
Marx's great insight was that all revolutions are driven by economic circumstances; a successful revolution is the resolution of contradictions* between the new means of production and the political superstructure and social production relations resting on the old means of production. A successful communist revolution will be the same: a resolution of the fundamental capitalist contradiction between socialized production and private ownership. Economic contradictions have an enormous effect on social relations: no amount of propaganda or indoctrination can save any social structure when it is fundamentally in contradiction with the physical means of production.
We can look back on the bourgeois revolutions of the 18th century, especially the American and French Revolutions. These revolutions introduced capitalism, and capitalism has... ahem... some serious flaws, but there is no doubt that the bourgeois capitalist governments were a dramatic improvement to a large number of the non-bourgeois masses relative to monarchism. Why? Why did, for example, George Washington not become King? Why did the French revolution devolve into the Reign of Terror and the restoration of the Monarchy, and how did the modern bourgeois French republic finally evolve?
Nascent capitalism started to affect the social-psychological-economic dialectic before the bourgeois revolutions. The social changes wrought by this dialectic formed an important basis of support for the bourgeois revolutions, a basis that could not successfully be discarded. The Americans preserved "bourgeois rights" and prevailed; the French initially abandoned bourgeois rights, leading to the Reign of Terror and the restoration of the monarchy. It took until 1870 to create the Third Republic in 1870, which preserved bourgeois rights and thus was able to survive until the German invasion.
It's important to understand that neither the Russian nor the Chinese revolutionary governments were brute force tyrannies: both enjoyed broad popular support without which they could not have survived more than a dozen years. They really did deliver on a lot of their socialist promises, and the social and psychological groundwork laid by nascent socialism were an important basis of support for the governments. To the extent that the Russian and Chinese revolutionary governments unjustly persecuted people, they did so at the behest and with the consent of most of the people — had they not enjoyed popular support, their persecutions would have caused another revolution. Even Stalin, who probably perpetrated the most unjust persecution, is still enormously popular in present-day Russia. (We hear almost exclusively from the Chinese intelligentsia, not the people. The Chinese intelligentisia dislikes Mao for good reason: the pre- and post-revolutionary intelligentsia enjoyed and continue to enjoy enormous economic and social privilege, which could not be maintained under socialism. But Mao seems to be popular among the few voices of the peasantry and proletariat we manage to hear.)
Nascent socialism is already making itself felt in the social-psychological-economic dialectic. There are many socialist rights already embedded into the social constructs and psychological character of individuals in capitalist societies: the contradiction between social production and private ownership is a powerful force in this dialectic. Regan notes that Canada "is arguably soft communism in action." Unions, business regulation, government health care, economic stimulus: all of these ideas are partial and incomplete resolutions of the contradiction of capitalism.
(And all of these ideas are bitterly fought by the capitalists (with a lot of success over the past 30-40 years) because they know these ideas undermine popular support for their own privilege. During the Great Depression, Treasury Secretary Andrew Mellon voiced the "pure" capitalist position: "Liquidate labor, liquidate stocks, liquidate the farms, liquidate real estate. ... [Panic] will purge the rottenness out of the system. High costs of living and high living will come down. People will work harder, live a more moral life. Values will be adjusted, and enterprising people will pick up the wrecks from less competent people.")
A successful socialist revolution will not come because some small, secretive group manages to seize power. A socialist revolution will come only when the socialist rights already embedded in the population undermine confidence in the existing bourgeois capitalist state, and the people, on the basis of those socialist rights, give their support in large numbers to a socialist organization. A revolutionary government must rise to power on those socialist rights; if it subsequently ignores them, the government will fail almost immediately.