No one can determine how long a war will last. They may see one side dwindling in numbers which may give them an idea that the war is coming to an end. However, any battle can strengthen one side and cause great damage to the other.
In several past wars in America, the war began with one side winning the battles, but then it turned when the other side started winning the battles until they won the war. Today, it does seem that ISIS is weakening due to the strong forces of the countries doing everything they can to fight ISIS and this has been going on for many years. However, since this has been going on for many years, it is hard to believe that the end is near.