Some really great observations and evaluations, IMO.
You make a great point about how Goff will get on the field. I expect that the offense will stall, and we will lose games because of it, but not because Keenum is the weak link. We all know where the real weak links are in this passing game. But yeah, they will have problems scoring enough points to win and Fisher will use that as an excuse to get Goff on the field.
I'm not sure when that will be. It could be as early as game 5. Or it could be much later when it becomes clear to all the players that they aren't making the playoffs again this year.
The question I have is when do the players come to the conclusion that they aren't going anywhere with Fisher. I mean, how long can he con them into believing that they can make the playoffs under him after 5 years of losing records?