This is not necessarily true - Nietzsche's Eternal Return may still live on due to quantum effects and statistical dynamics. While theories such as the Big Rip or Big Freeze have taken precedence over the Big Crunch, there are mechanisms by which the universe could return to a state of complexity rather than a soup of electrons, positrons, neutrinos, and photons, even though it has winded down to the Dark Era of the Universe.

The most notable of these mechanisms is Poincare Recurrence, published by Henri Poincare in 1890. The concept of the Poincare Recurrence Theorem is rather simple - given infinite time, systems return arbitrarily close to their initial states. The classic example is that if you open a new pack of cards and shuffle them many times over, the cards will eventually return to the order in which they were initially.

Because the conditions that led to the universe entering the Dark Era are reversible, thanks to Einstein's good old E=mc^2, physicist Don Page has calculated that the universe is estimated to return to its current state after 10^10^10^10^10^1.1 years. The exact timing however is not particularly important, because given sufficient time, highly unlikely events become inevitable.

There are also apparently quantum mechanical events that could generate a new big bang, which would occur considerably sooner than a Poincare recurrence, but the details of which I am not familiar with. This comes in at approximately 10^10^56 years. These events and more can be found on Wikipedia's Timeline of the Far Future.