You had a fatal loss accident and your insurance estimate came out to be significant less than the residue value for your leased vehicle What is your recourse How do you negotiate with my insurance co?

You might well be on the hook for the balance. When you leased your vehicle you should have taken out "gap" insurance which would have covered this "gap" in coverage you have just described. Many times whoever leases (or sells) the vehicle will offer this coverage during the sales closing process. Double check your lease documents to determine if you're covered or not.