If Jack flips Mark a lot more than Trump will have to worry, many conspiracies and schemes involving lot's of republicans will be an open book, many with receipts. Mark was conspiracy central and when he cuts a deal with Jack he has to confess to ALL his crimes and any other crimes by others he has knowledge of. Jack won't need a deal for Donald's ass, because he already has it over the documents and it sure looks like he has Mark's ass too. Maybe flipping Mark and debriefing him is part of the recent delay, they want to use Donald's first indictment to shake loose the rats over J6 and Mark was in on everything. Mark might get a deal from the feds, but he will still be facing state time in Georgia, serious time for election conspiracy also involving the fake electors. So maybe they will make a package deal where he testifies in both federal and state court against Trump, in Georgia it will be on TV, so that has got to be worth a deal there!
BTW: Mark knows every congress person who requested a pardon and there may be more than we know about, those are knowledge of crimes by others too...