if the universe is expanding like a wave, will it return like a wave returning to the sea and cause another big bang event,
A wave is pushed onto the land from all that wind energy it accumulated. That push (kinetic energy) takes it only so far up the shore whereupon gravity draws it back into the sea. Similarly, as you suggest, this same force (ie gravity) has the ability to pull all the universe back to that beginning point, but only if something isn't preventing that from happening. What was discovered (serendipity) was that the universe isn't slowing down as it expands, but speeding up. Using your wave analogy, the initial expansion should be noticeably slowing down as it converts all the initial surge energy into potential energy. What they found was that the universe is accelerating, as if -- using your wave analogy again -- the wind has gotten stronger and is pushing water onto the shore with no return. No one knows what this "wind" might actually be, but they can't see it directly (hence why not call it dark) and it must be an energy-like something or other to overcome gravity, so they call it Dark Energy.
McDonald Obs. , in the last several months, is now doing a major study in understanding more about DE. They are using their modified 9m, or so, telescope with incredible imaging from its 35,000 fiber optics coming from their huge camera sensors.
if so, could the purpose of the current life forms be to break through the returning wall of reality to the primordial nothing that was before
It's hard to imagine any good purpose associated with a collapse of this universe as temperatures will reach in the many billions of degrees before any hope of a break through.