I believe it works something like this:
Sid works with an assistant - maybe more than one. Sid (or so I believe) tells them what he wants in the column, and the assistant does the actual writing. Of course, most of the columns these days are just transcriptions of interviews. A lot of them are pulled from interviews on the Sunday Sports Huddle, or interviews that Sid, or an assistant, does with available coaches and players.
As far as not having as much Gopher material - a lot of the Gopher practices are closed, and there is not much access to players, so Sid (or his assistant) don't have a lot of available audio to transcribe for the column.
It's all a way of keeping Sid's brand active in the paper. Because nobody has the guts to tell a 97-year-old legend that he should retire.