I'll just add that he may not have played his last game for Cas. Obviously there will be no miracle cure before season's end but he isn't retiring. Therefore, there is a possibility, like so many who have left Cas, that he comes back to to play for us at some point.
Anyway, injuries like this are unlucky and you feel for the player involved so I hope he recovers. However, I won't wish him the best until a day he does come back...