today I am coming with second option for end of our Universe. This one is probably little better since there is nothing ripped apart.
Because most of stuff which is going on in our Universe happens in stars, atoms are slowly decaying into radiation.
That is because of process called thermonuclear reaction which is happening in all stars. Below is scheme of what is going on when two hydrogen atoms merge up together at very high temperatures. Most of energy is decayed in form of gamma rays and then some in neutrinos. This stuff will eventually fly around and it wont ever be used up again.
After lot of generations of stars there will be no more gas to form new ones and all of the energy will be equally spread out which would mean maximum entropy in our Universe. No new reactions and nothing more happening here.