captainsolo said:

It seems like it is our only source now. Even George wants to use it as the base of all reference.

You would be correct that it was used as the source for color correcting the 1997 version of a new hope since the original negative was so badly faded.

But i also believe that Lucas has separation masters for all three original films.

These are called protection masters because they can be used to create a new negative if the original is lost or destroyed. The quality is not as good however.