He could have written a pardon late on the 19th or morning of the 20th, and they wouldn’t have time to impeach/convict before his departure. Whether or not his chain of command would have still taken orders from him anymore between Jan 6-20 is irrelevant. Courts would later have been forced to abide by a lawfully issued presidential pardon, and practically all of these kangaroo court cases could have been prevented.
If McConnell and his cronies convicted him out of spite over the pardon, he could have appealed to SCOTUS since impeaching departed presidents is technically illegal anyway. He just didn’t want to risk his political future over saving these people.
Tarrio wasn’t even charged until March 2022. It’s not like there was a list of people who have been charged handed to Trump so he could name them and get a pardon for them before he left Geez get a clue.