They have been fighting for several years and appear to be holding up against Russian forces, so I think that will continue. Other countries in the area have strong motivation to help them if assistance is needed in order to stop Russian aggression, so I think they will be successful ultimately.
Russia is a very powerful nation, and the Ukraine is very small in comparison. Russia is hedged to become as powerful if not more powerful than it was during the cold war era, except this time it will be by brute force. Ukraine does not have a powerful enough army to defend itself.
The fighting in Ukraine has been vicious for quite a while. Judging from the ease in which Russia was able to take Crimea, Russia has the power to continue to wear down Ukraine. However, at this time Russia is focusing on the situation in Syria, which may give Ukraine some time to gain strength. Ultimately, the outcome will depend on Russia's international relations.
Russia has an unparalleled military might in the area and they are fresh and confident that the U.S. under Donald Trump will not interfere with their expansionist tendencies. I fear that the Ukraine will not be the last nation to fall under some flimsy excuse for Russia to invade a sovereign nation.