You don't bench a QB when your team is winning unless the guy coming back from injury is an All-Star and clearly much better than the current guy.
Fact is, while Teddy was playing good back in 2015 its wasn't appreciably better than Case and can easily shown to be slightly worse.
The only reason they would do this is to ensure Teddy gets some meaningful snaps before they have to decide on who to keep in the off season. However, Case has now shown them that he can do pretty much exactly what they were paying Teddy for...and would have to pay Teddy a lot, lot more since he still might hold some of that '1st round pick' cache/value.
The Viks have three QB's with contracts ending. Going to be a wild off season for them.
Sam is on IR and done. Does it make more or less financial sense to have Teddy sit on the bench while they play Case's hot hand or let him in and let him prove what he can do? Another question is, will Teddy be the 'team player' he is now when its the off season if he didn't get that chance to prove himself again? If he thinks the reason was financial though then I doubt he'd be very happy come the off season. Going to have to know his ego and it might play a part of their decision.