If there were a way to audit ballots by tracking them back to the voter to determine if "vote harvesting" occurred... and it showed that it had not and if all votes were discarded that came in after the official due date, I think Trump would concede if he still lost. Do you think there is any chance of that?

No one knows, now have stated that have been prevented with evidence of vote harvesting made any really attempt to measure how much took place. Trump may well have lost anyways... but there is plenty of evidence that vote harvesting occurred.