Afaik head to head stats would the one to be used as tie breaker if points are equal at the end of the group stage . If PSG is to fail tomorrow means that both PSG and MU has 9 points, but PSG is leading head to head by 2-1 and 1-3 means that PSG will stay on 2nd position no matter what is the result of their match against Basaksehir. Correct me if I'm wrong.
Yes you are correct. PSG are leading right now with better head to head stats. It was all from the left- wing back Angelino who was heavily involved for Leipzig. Leipzig knew how crucial it was but United thought it too easy and Ole thought it differently and his side got kicked out of CL.
Now looking back at things, United were leading the group but in later stage got thrashed quite badly in last two CL games against PSG and Leipzig.