I have seen a tank repaired without replacing the piece of glass, although it was a 75g not as large as the one you are looking at.
The interior silicone was removed from entire tank. A piece of 1/2 glass was cut to fit inside the tank against the broken piece(cut to fit thight). The broken piece was then skimmed with silicone and the new piece was placed against it and let cure. The entire inside of the tank was then resealed with silicone.
The crack in the end glass of this tank was approx 24" in lenght. It went from front lower corner to the back upper corner.