The ONLY player on any NFL team where I would agree with the general sentiment of 'can't recover from that loss' is the starting QB.

If you can't weather the loss of one edge rusher - if you are THAT reliant on that one edge rusher to provide pass rush, and without him you have none - then your team must not be very well constructed. Either that, or your coordinators are incompetent and can't adjust schemes to cover for the loss of one player. Not saying it would be just "no problem, easy peasy" - it would be incredibly tough, and would certainly require some other guys to step up a level or two. And yeah, you'd probably lose a game or two that you might have won if you had him. But if one edge rusher means "season over - won't win another game", then what that means to me is that you have an awful football team that just happens to have one premier edge rusher.