While @idonotlikeusernames’s politics gives me visions of Robespierre’s Reign of Terror and Stalin’s forced collectivization, induced famines, pogroms and purges, he’s absolutely right that the nobles will turn on a helot MC once the Hegemony is defeated if the helot MC doesn’t meekly accept a token title and sell his fellow helots out. The helot MC is at a decided disadvantage here, especially if he or she eschews the legitimacy that co-opting the church would give him/her. I think a “Third Estate” alliance between the helots and merchants would be key to checking the nobility as the merchant class has the wealth and the logistical know-how to keep the helots supplied and fed, as well as a strategic interest in increasing their own social standing and independence from noble dictates. Any helot rebellion that alienates the nobility, church, -and- merchants is doomed to failure. The helots may have numbers, but they lack the organizational skills or know-how to build anything lasting.
Only having support from one of these three educated groups is liable to be extremely expensive however, and potentially disastrous, as they selfishly milk you for every concession they can get when your ability to say no is limited. It’s much better to pull support from at least two if not all three of these groups so that you can play them against each other and avoid getting overly beholden to, or strongly opposed by, any of them. Unless you meta-game however, for an uneducated helot MC, this is much more easily said than done.