When the check arrives, the administrator of his estate will be able to cash it. An executor or administrator of an estate that has been appointed in accordance with applicable State law may endorse checks issued for payment of tax refunds, among other things.
If no administrator has been appointed, you must return the check to the IRS with a request to reissue the check and a copy of your father's death certificate. IRS Form 1310 (a link to the form is below) was created for this purpose.
My condolences on the loss of your father.
https://www.irs.gov/pub/irs-pdf/f1310.pdf
