The governor is irrelevant. His certification is not a constitutional function, just a ceremonial act delegated to him by the state legislature.
If the election was not conducted according to the rules set forth by the state legislature, then the legislature has every right to send an alternate slate of electors.
In all likelihood they can declare an alternate slate, especially if the courts determine that the election was so fraudulent as to be invalid. But that is not the case here. The legislature did not appoint the GOP electors. The courts have not ruled the election to be invalid. This is a case where the electors are proclaiming themselves to be electors. Where does their validity come from?