The revolutionary approach doesn't necessarily allow improvements in the living standards of the working class to be kept either, as we well know. Even in Cuba the regime is implementing plans to roll-back egalitarianism, reintroduce the lash of income disparity and the market.
Some gains are relatively permanent - like literacy, which remains an achievement in China and Russia. But then this also seems to be a permanent achievement of the reformist left in capitalist nations as well.
So, we can say that neither the reformist nor revolutionary approach makes any guarantees for gains and concessions won by the working class. But, then, when are there ever any victories in politics or the class struggle that are won for all time?
Finally, it's an open question whether the changes won by reformist social democratic, labor, and liberal parties are ever entirely stripped away. From an Olympian vantage point, it may be that the working class is simply experiencing a case of two-steps forward, one-step back. We may never return to anything like the conditions that prevailed when Englels wrote The Condition of the Working-Class in England.