The late window game (4:25pm ET) almost never concludes in time to run a postgame show. Should it run slightly short the game broadcasters will fill with comments and player interviews. Also remember that CBS usually has a second, and sometimes third regional game airing in the late window, and will send viewers to the conclusion of any longer running contests.
CBS has to keep 60 minutes at its usual length as any variation would screw up the west coast prime time feed which runs in a “normal” pattern starting at 7pm PT.
You are assuming this can be done on the fly. Technically possible if you want to have a live crew editing, assembling, and playing out the show in real time. But usually the final edit of each complete 60 Minutes episode is finished in advance of the broadcast.
Years ago CBS would send a preview of the entire completed 60 Minutes show down the network line late Saturday evening. Don’t know if they still do that.
Again the west coast issue comes up. If the CBS east coast prime time were to run more than three hours but less than four hours, then what do you do with the west coast which is scheduled for four hours?
Now if a late window game runs up to 8pm ET, then CBS sometimes will drop the final prime time show for the east coast feed, which gets local news back on time. West coast affiliates will still receive a four hour prime time, replacing the show that was dropped from the east coast feed with a rerun.
Delayed Sunday prime times on CBS have been going on for decades, and 60 Minutes viewers are used to it. Doesn’t seem to have affected the popularity of the show.