You can rest assured there will be no way to access the data once the phone has been reset. Apple have designed there phones with security at the top of their list. There is an IC on the logic board called the “logic eeprom” it holds all the keys necessary to access your data, when the phone is reset so are the keys. Even the most sophisticated forensic software used by the law enforcements would not be able to access the data once the phone has been factory reset.