I think there re some circumstances under which we can loose Harrison. But those circumstances entirely depend on how big the change in GAM for a player sale to a foreign club are. If the GAM allowance becomes something like a straight 90% then I believe we would probably loose jack.
That said, Jack probably wants to play for the USMNT as its his only realistic shot at international soccer. So if jack signed the right deal with CFG and made a firm commitment in the USMNT direction, I could see them trying to work out a method by which he can stay. But that entire deal is basically a hedge on how valuable a USMNT player can be to a club for reasons extraneous to his actual ability to play soccer. Put it simply, dortmund have seen way more financial benefits from having Pulisic on their team than would otherwise occur for a random high level prospect.