I don't know whether or not you should TIE the last game (Because you REALLY want home court advantage against the other 1st seed) but you should make sure you maintain a higher PD than him. As for if you will promote with a 21-1 record... Probably not but there is always a few exceptions where almost every 22-0 teams win their divisions which leaves one or two openings for 21-1 teams, but it isnt likely. I simply suggest that you do what prepares you best to win your league rather than hoping for bot cleanup. Best of luck.
Sincerely,
Another IV manager with a 20-1 record.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs