Based on the Big Bang Theory of the Origin of the universe, the universe is expanding. So there is no prospect for it to end. Astronomer David Levy says that half the mass of the universe is missing. If that mass were intact, the universe would collapse into nothing, which might be its end. I have a Hub "Big Bang Theory (Origin of the Universe): What Is the Mystery?
The Gregorian calendar or Chinese calendar cannot be used to recon the origin or the end of the universe because they are inventions and they do not have any physical reality. Time is not a physical reality. In the theory of relativity the physical reality is interval.