In each case the outcome is different, and the classes arise again in a different form on a slightly different basis.
For instance, European Feudalism ruined both classes -- when local peace held for too long and war became more commonly national in scale, the truly feudal Lords eventually ended up landed but penniless and the truly feudal serfs wound up without any source of protection. So both were either driven into towns, with that new set of classes (bourgeoisie and proletariat), or folded up into the wider holdings of the mercantile era nobility, with that new set of classes (state taxpayers and tenant farmers). There was no revolution because both other options already existed -- the upper nobility was already mercantile and statist and the town system had always existed to deliver goods. But two things that had been minor contributors came to center stage -- Nations and Cities.
That is the synthesis part: new options become visible through the pressures of incipient failure, to either solve the same problem more broadly or to mine a new vein of temporary options until a broader solution takes hold.
As I see it, it parallels the development of industrial power. We try out each different potential basis and reason for the class division, using up or outgrowing the 'fossil fuel' implicit in that mode of contrast and its associated virtues and moving on to the next form of what we currently model as social capital (but only because we are capitalists), until we find a social organization with a renewable form of 'social energy', or we run out of options and simply succumb to directionless and chaos.