If we reverse time and take this universe in past, like x years ago, what are the chances...

...that it will result in the same universe, as it is today?

50%? 100%? 0%?

I'll put it this way: say we had two universes exactly the same in every respect. Would they have the same futures as well? No, because although the same conditions exist and the law of causality should result in the same chain of events in each universe, quantum uncertainty is also a factor. Quantum uncertainty does not follow the law of causality, so the two universes will diverge from one another at an exponentially increasing rate. The Butterfly Effect would result in two very different universes in just a short amount of time.

Changes? Chance? Well if you talking some milisecond into the past there would be no changes that will meet your eye. But about 13billion years back? Well there would be an upside down picture of our universe waiting for you. Galaxies were yet to form, few stars or no stars at all. Primoidal gas clouds everywhere, lots of radiations, that's the picture. But if you talking about only the time reversal, well in that case our picture of the universe would not change at all, because physicists showed that entropy of the universe will go on increasing even if you reverse the direction of arrow of time. And by the way no one can travel into past so don't take tension. Our universe is very beautiful as it were in the past, are in present and will be in the future.

It depends what you mean by "the same". If you mean the same down to the state and position of every particle, the answer is zero, because events on the quantum scale are probabilistic and there is effectively an infinite number of states all the particles in the universe can be in, so the chances that we would get to the same set of states is effectively zero.

On the macroscopic scale too the rerun of the universe would not give exactly the same results, although you would probably have to start further back in time to see any noticeable difference.