Now that I *THINK* all the NFL defections have been declared, here is a look at Ohio State's Offense heading into next year:

It appears that the Buckeyes will have six returning starters on offense and a total of 14 returning from the 2-deep. Going by position groups:
QB's:
Having a Heisman Finalist returning at QB is pretty much as good as it gets. The departure of his backup sets up a battle for the #2 (who will presumably be #1 in 2021) but shouldn't be a big issue.
RB's:
Obviously losing the School's single season rushing record-holder is not a good thing. IMHO, Teague is a decent back. He is very physical, so much so that I might actually prefer him over Dobbins in a 3rd and 1 situation but he lacks Dobbin's speed. In the CFP semi-final Dobbins had a 68 yard TD run and a 64 yard run that was oh-so-close to being another TD. Those were just run-of-the-mill plays but he beat one guy and had the speed to turn it into a LONG play. In those situations Teague would have been more likely to run for 20-30 yards due to having less speed in the open field.
WR's:
The Buckeyes are losing two out of three starters and three of the six in the two-deep. That said, WR is a position of depth at tOSU so this shouldn't be a major problem. Olave, Wilson, and Gill are a quality group and have seen plenty of playing time. The WR's should be fine next year.
TE's:
The starting JR and the backup SO are both back so this position should get better.
OL:
The Buckeyes are losing two out of five starters and three out of 10 from the 2-deep. At this position where youngsters rarely see the field let-alone start that isn't too bad.
Overall I think that tOSU's offense should be at least close to as effective in 2020 as it was in 2019.