knowing insurers that will be an excuse not to pay
All you can do now if file the claim and see what happens. The insurer has every right to deny the claim as they have the right to inspect the damages. Unfortunately since the repair work is complete they have no way of verifying the cause of the damage. However they could also be satisfied with the report the contractor you used can submit as to the cause of the damage and pay the claim. It's a coin flip at this point. Next time call your insurer right away. You can call workmen in to prevent further damage from occurring but you went too far in this case.