Why would Rob Ryan be canned? Even if Garrett gets fired there is a very good chance that Ryan is retained for the next coach.
Even at 4-5, Dallas has a top 10 defense and thats with at least 2-3 players out on defense. Ryan has done his job, but Garrett looks to be on his deathbed.
That's generally what happens when you hire a new coach. They bring in their own staff. If Jerry Jones forces a coach to keep Rob Ryan he's going to have a very, very short list to choose from. Plus, rumors are already circulating about Rob Ryan and college head coaching jobs. I can't imagine he's going to wait around, just in case a new coach keeps him.