Forrest, this is the most illogical theory to date. Aside from the fact that Balor's head was cut off and The Head is a severed head.. there is absolutely NO evidence supporting this, and it takes an extreme amount of explanation to refute the solid evidence presented below:
a) Balor has his head on.
b) There is no time travel that we know of in myth.
c) Why would the head do things which would lead to his own defeat?
I'm sure there is more, but you get the picture, there is no way this was Bungie's intention.
-Milky