Anybody can get hurt, but it's unlikely a young, sturdy buck like Dak is going to get injured long term. If he does, Romo will be back. You can book it. What could get interesting is if Dallas is floating around .500 and Dak is struggling and costing the team games. He's still very young, so that's possible.
Romo simply doesn't want to start over somewhere else. This is the team he is tied to whether he's played his last game or not. I think that was the reason for his ultimate decision.
It's just like last year, but instead of hanging on the sideline, Romo is hanging out in the broadcast booth a phone call away.