We all know the consequences of scrumming, and tackling etc. its a part of the game, you do what you can to minimise by perfecting your technique, and wearing protection if appropriate. (personally don't like headgear - as i overheat too easily - tape around the ears all the way)
Everyone is different in their reactions, personally, I knocked myself out playing touch footy once (head to knee) I was fine, and played in the second half, and basically felt nothing different after the initial 5 min or so. Others have gotten knocked out and been out for weeks/months/careers.
There should be an independent panel (non-club/union aligned) to look at concussions, as you can be fine to play on, or need to have months off/never play again. You can get knocked out or concussed, by slipping on a banana peel, not playing rugby will minimise the chance of it significantly though.
Overall - smart move by an experienced player, he's got plenty of years left to play, and wants to play them out.
Trav