At this point, if that really is AD's official position - then it is time for the Rams to harden. They hold the leverage and AD's - I won't play another down position is entirely illogical. Keep your best offer on the table - always be willing to welcome him back if he is ready to become the highest payed defensive player in history and show up - but tell him that you have a team to run and if he doesn't show up for this season, that you will begin working on Goff, Peters, and possibly extending Suh. If by the time AD decides he wants to play again, the cap situation has changed, then the offer may get worse. He can still come play out the rest of his contract and play under the tag - or he can waste a few of his prime out of football. AD just doesn't have many options other than to threaten retirement - which is a non position.
If I am the Rams, offers don't improve from here.