If it were mine, I would send it in to be repaired and refurbished. There may be internal damage from the impact that is not apparent to the naked eye. With that visible damage the value of the lens has plummeted. Having it repaired and refurbished would restore it's value. The 24-70 is an excellent lens, and well worth repairing.
Sending something in for repair that appears to be working just fine just seems absurd to me. And what's this nonsense about the value of the lens plummeting? The lens is just a tool, not a collectors' item. Value is based on its usefulness to the owner.