Buy it back. Even if you are unable to repair it the parts are worth much more than they will reduce for the buy back.
Contest the insurance company on the value of the bike. Their first offer is generally a lowball and they are usually willing to adjust.
Buy it back. Keep it in your hands. The work pon the engine is worth probably more than the buy back cost.
This wasn’t the Attic Rat bike. That would have been a real shame!