I expect that the "free" dining plan may be gone for quite some time. I wouldn't expect it to come back, if at all, until 2023.
The paid-for dining plan I expect may be back in late 2021 or some time in 2022, as the 50th anniversary celebration, the lifting of attendance restrictions, and the willingness of people to come to the parks, come together to drive Disney to open up the remaining dining venues.