If insurance company sends a check for roof replacement and one get it 'fixed' does he has to send the money back to insurance company?

Most policies will pay for roof damage on an "Actual cash value" basis until the roof is replaced. Then, IF you have replacement cost coverage they will make up the difference of the amount paid under actual cash value and actual replacement cost, LESS the amount of your deductible. If you elect not to repair or replace the roof, your insurance company could exclude your roof from further damage or additional payments until you show the monies paid to you were used to repair or replace as indicated by their estimate and claim payment. Otherwise, the money is yours unless the home is mortgaged. If it is mortgaged, the check should have been made to you and the mortgagee, and if the mortgagee endorses it it is yours.