[ZenGum]

IMHO the current accumulation of complexity is an enthalpic * state created by skimming off a portion of energy as it flows from one form to another. This is what life does, how it sustains itself.
Eventually, as universal entropy increases, such energy flows become scarcer, life will starve, organic remains will break down, and complexity will greatly diminish towards the heat death of a wholly random universe. I guess there might be remnant complex structures that need a bit of an energy shove to make them break down.
However, I also favour some kind of oscillating universe model, probably not a bang - crunch - bang model but a bang - stretch - fade - quantum bang! model. Complexity will rise again!



*enthalpy. opposite of entropy.