They might extend Diamond for this reason, but I'm guessing they won't because you already get a full extra year with it (well, an extra year if you earn it via play, and do so early in the year.)

The people who are really going to get fucked are the ones who earned it in December 2019. Theirs expires in January 2021 and they will barely get benefits out of it.

Guess we'll see. Maybe they'll tack on an extra year anyway, just to entice people to come back and prevent complaints/frustration over earned status being "wasted".