Not sure if the normal separation rules for parallel approaches apply once you have VFR flights involved? You pass the traffic information, then the pilot is responsible for separation.
To some earlier post..... the Metro was on short final, what would you gain from telling him a part of his fuselage is missing? He wouldn't go around.... and there are no real checklists to complete in this event.... if anything, a quick landing is probably the safest anyway.
Did the controller see the collision? She could've had her eyes elsewhere for a second.