If the airline denies the claim nothing happens, at Airning we will always try to fight for your case, so we will follow other ways to get the compensation.
We will process the claim before an international agency that is in charge of the fulfillment of the obligations of the airline. The only thing that will imply will be a little longer since the term increases significantly, but nor would it have costs for the client.
For claims denied, the total term is estimated at around 6 months maximum.