Once your dad's I-485 has been properly filed and acknowledged, he will be considered in status even if his I-94 expires. Make sure that you have all supporting documentation available with the applications (birth certificate - yours and your dad's, your dad's marriage certificate, etc.) Youd dad will also have to complete a medical exam from an approved doctor and obtain doctor's report as part of I-485. The medical exam can be done later when USCIS requests for it (you will be sent an RFI - request for evidence).