First of all, the assumption that everything will return to its original state is a theory of Aristotle that was debunked centuries ago.
The actual theory does exist, with the nearly infinite gravity and such creating a perfect sphere smaller than the smallest particle and booming again.
There are two other possibilities though:
There is the possibility that the explosion had enough energy that it will eventually lead all accelerated particles to escape the original locale's gravity, leading either to the dispersal and ultimate downfall of all energy that exists or to separate smaller universe origins occuring with matter and energy that becomes attracted to other "forsaken" material.
The other possibility is that the heat and light energy that does escape from the original gravity's pull will have an effect on the next cycle and cause each concurrent universe to be ever so slightly different. Life on earth, or even just humanity could only get a single run at this crazy game called existence.

One more thing: religious people have already bastardized that theory to state that god set the cycle in motion and uses it to test humanity repeatedly.
Religion is like a cockroach, or a bacterium: as long as it has a medium, it will take it over, make it its own, and shit out something nobody really wants to touch.