When the top of a tree dies it means the active growing ends of the roots have died and the root system cannot take up enough water to sustain the tree. These trees will continue to die back over time. Your tree foliage looks very thin and the prospects going forward are not good. There may be some cankers or rot developing in the upper canopy of the tree too which makes the wood vulnerable to wind breakage.  You could have the top of the tree removed but of course that ruins the shape and appearance of the tree, and it probably wont help the tree live that much longer.