Perhaps they pass some reforms that strengthen the Republic and make it less susceptible to civil war and dictators?
What sort of reforms? They can imitate the steps taken by Sulla and tighten the oligarchal structure all they want, but it won't change the underlying social and structural problems the Roman Republic is facing by this time. The military has grown big enough to control the outer provinces but therefore way too big to
be controlled, strongmen of both conservative and populist stripes have already arisen (and even succeeded, as this is after Ceasar's unchecked dictatorship), and corruption is already an integral part of the Roman state.
The Liberators winning the war against the Populares would likely just lead to their cause being coopted by Lepidus, who, as a very indecisive figure, would probably just ignore the problems for a while until another Caesar rises and properly adresses them. Barring a sudden territorial collapse in Rome's Mediterranean empire, i don't see the republic surviving in its original constitutional form any longer.