Let me put your minds to rest if you`re worried, the End of the universe will not occur for a long time. When I say long, I really mean long, there is not enough bandwidth to say how long it might be. There are a number of competing theories of how the universe end, only one can be right but because its so far in the future, we won`t know. Here is a guide to the different theories. They are all named have Big in their name to signify how much it will affect and also a nod to the The Big Bang which started it all. If you`re looking for just the end of Earth, you should look at End of Life on Earth.
When the Universe started, there was an enormous amount of energy that pushed matter from the centre. As you know when you throw a ball, the ball will stop when it runs out of energy and fall down. The universe is expanding and once it gets to a certain size, the energy will have run out and dissipate. Matter once destroyed does not return back as it was before, the Universe will end into nothingness. According to Professor Brian Cox in his Wonders of the solar system/Universe series, he says there are not enough atoms in the universe to represent the amount of years left until the Universe has completely gone. Even then, he says the universe will have free particles still existing. The Universe is only 13.5 Billion Years old, it still has the vast part of his life ahead of us. No human alive today will see the end of the universe unless of course Doctor Who exists and takes someone to Malcassairo, the last planet in the Universe in the episode Utopia.
We are currently in the Stelliferous Era, the age of the stars. In cosmic terms, this is short compared to what lies ahead for the Universe. The largest era of the Universe will contain black dwarves and black holes and they will be known as the Degenerate and Black Hole Eras. A Black Dwarf is a White Dwarf which has run out of its remaining energy. There are no black dwarf stars out there in the Universe because they takes billions even trillions of years to form and that the Universe is too young for them to appear. Eventually the time that stars existed will be no more than a blink in the eye.
The theory states that continued expansion of the universe will cause the fabrics of the universe to tear apart. If you fix one end of a piece of string to a stationary object and pull the other end. If you use enough energy, the string will break. This theory is about the Universe expanding so much that it rips itself apart.
This theory states that when the Universe gets to a certain size, it will begin contracting. Take an elastic band, pull it apart as far as you can then let go, it will return back to its former size which in our case will be the singularity in which the Big Bang started from. I am not suggesting you try the elastic band experiment because you will if you do it wrong will HURT yourself. If the elastic band breaks because you`ve pulled it too much, then your elastic band universe has destroyed it self in the Big Rip. As to how the universe will contract, the ideas are endless. One unlikely scenarios is that we live life back in reverse, instead of life to death, it`ll be death to life. In the television series Red Dwarf episode Backwards, the crew visit a planet which everyone is doing things in reverse although the crew do things forward like we do now.
The Big Bounce is an additional step to the Big Crunch, in that once everything has contracted back into a singularity, the whole thing starts again, a new Big Bang. There is nothing to say that this has not happened before as its a theory and hard to disprove. We could be locked in an endless birth, death, rebirth recycle. As for whether you`d do the same thing again, I couldn`t possibly say. As the Universe is not perfect, all it takes is one atom to be out of place and things could cause a different future on the bounch back out, your atoms might not end up on Earth next time.
There are those who believe that there will be no end to the Universe, that the Universe will continue for every. The theory is known as the Steady State Theory which says matter lost is replaced by new matter. The Universe has no beginning and no end, the Universe is here to stay.
You can read further into this at Wikipedia.