I think what was supposed to happen was when Sanchez went in, he was only going to play a series. If he led the team down the field and scored, he most likely would have come out. Since he sh*t the bed and fumbled the shotgun snap, they trotted him out for another series, where he wound up getting hurt.
I hear you, except here's the issue (and I'm not one of the hardline Rex bashers here): there was no earthly reason to put Sanchez in there.
Sanchez was in do-no-harm mode and in that role he fumbled a simple snap - his third ridiculous blunder in as many games - and he was STILL going to get the job. So unless he sat on the ground and sh*t himself and rubbed it all over his face, the competition was over. If Sanchez screws up and STILL wins, then there was no purpose to inserting him in the game (backup OL or not). I mean, literally unless Sanchez threw a pick 6 or two in his 1 quarter of work, the job was his. So why is he out there? To "win" a job he's already won? It makes no sense from a logic standpoint.
There are only 3 reasons to put him in there.
1. To watch Sanchez succeed and give a definitive end to the competition.
2. To win a meaningless preseason game (no matter how much coaches bluster how every game counts and you can't get used to losing and blah blah blah. It's a preseason game and it doesn't count, end of story.
3. Rex is not convinced that Geno is unready to start week 1.
So I'm not satisfied with either of the first 2 reasons, and don't believe the 3rd reason. If reason 3 was true, then Rex's podium dance would have been different. He would have said all the appropriate "this sucks" comments about Sanchez's injury but he would have said he still felt good about going with Geno week 1 if the injury forces him to, because the competition was neck & neck anyway & was so close you could flip a coin and not really go wrong no matter who it ended up being. But he didn't say anything like that. He was wearing the face of a guy who may have just lost his starting QB 2 weeks before the season starts.