the shelf life of a mobile qb is shorter for obvious reasons. he never developed touch and is inaccurate. once the athleticism started to go the wrong way there arent the passing skills in his game to fall back on. there isnt another qb out there with his style really anymore so i dont know where he could even be a backup. new england took a shot, likely their best option at the time but they will move on and if he finds another spot i would be surprised.
A midfoot injury can be devastating for a pro athlete. Some never really recover. Santonio Holmes, Maurice Jones-Drew, Ted Ginn Jr. are ones that I can think of who weren't the same after they had surgery for it. It depends on the severity. I think it's considered worse than an Achilles. It's very hard to come back from. Probably not a starter anymore after this year.