When Chris Bosh was unable to get cleared by the Miami Heat doctors last year, it was because no doctor would clear him due to his current medical condition (blood clots which require him to take blood thinners) that puts him at risk of serious injury and even potential death every game. He's not officially retired and is keeping his options open to potentially still returning to play basketball. My hunch is he's keeping up to date with research and pharmaceutical development in hopes of something that will enable him to play again.
With concussions, it's unclear how many is too many. If you play until the one that takes you fully out of the game, then you may be well beyond too late. While you're healthy, doctors can't exactly say, "you're x hits away from CTE or enduring severe long term symptoms so we can't clear you to play." It seems like players who leave because of concussion related symptoms do so not on their own accord but because they endured one final concussion that made playing an impossible situation.
So if we're talking about a player leaving the game before exhibiting debilitating symptoms, no team doctor is going to force Crosby to stop playing, leaving Crosby to make that determination.
But if you watch documentaries of professional retired athletes, many of whom are dealing with their aches and pains from their playing years, few ever gave up the game before they were truly unproductive players. It's hard to give up something you've been doing for decades of your life, something that creates your identity, gives you dignity, and is something you clearly love doing.
So it's only reasonable to assume Sid would only leave the game 'pre-maturely' (as in, before most fans would reasonably expect someone physically healthy like him to retire) if the symptoms were so bad that he couldn't play a full game or go out and live a normal life. It's completely in line with what nearly every athlete of every professional sports league with high visibility would do, be it in the NHL, or the NFL or even the NBA.
I think we have to acknowledge that if we're putting on the onus on Crosby to make that determination, you have to believe he'll either retire when he's too told or if symptoms prevent him from playing (e.g. from another concussion). If the latter happens, it's too late in the sense that severe brain damage has been done, it's irreversible, and will affect him for the rest of his life. But now we're at a point where we can legitimately say that doctors, the team, or the league could've stepped in and said "no, we think the risk of your long term health is too high, we really suggest retiring from the game for your own safety" instead of pretending that the onus was only on the player to figure things out and that future that will unfold over the next ten years is not preventable. Because we know exactly what athletes will do.
