not good news regarding the Mortgage. If you stop repaying the loan they will want to know why and start proceedings to recover their money. The facts of the fire and the habitability of the property does not "let you off the hook" with the Mortgage lender. They secured their loan against the property, but it was a loan of money that has to be repaid.
If the property were to revert to the Mortgage company because they wished to recover their loan, then any insurance pay out with respect to that property not yet made will be part of their ownership of the property. If you had insurance on the contents that is a separate issue.
Best advice it to get back on good terms with the Mortgage lender and make an arrangement to pay the arrears and catch up with payments to prevent the transfer of the property to them.