I am not even gonna touch the debating that has gone on so far in this thread. Emotions and allegiances seem to have been flaring from the first page. Who you support and who you don't shouldn't factor into this discussion IMO.
That being said, I do not believe MS will kill himself as Jackie Stewart says. Sir Jackie was an amazing driver, but he runs his mouth too much for not being employed within the sport at the moment and not having driven a modern grand prix car. He has been saying Michael should retire since after 2002 if I remember correctly (entirely possible I may be off by a year). Sure Michael is an ultra-aggressive driver, but what truly great driver has not been? I don't agree with the infamous Schuey-chops on Hill and Villeneuve, respectively. I believe Schumi is making more mistakes lately out of frustrated determination. His red car has not been the winner it was when he took down five championships in a row. MS is a man obsessed with winning above all. Look at how excited he gets when he wins (ok, I know we havent seen it in a while, and Indy '05 doesn't count in my book). He celebrates like it is his first race win every time. If he did not enjoy the competition, the driving and the atmosphere of the F1 circus, he would have stopped already. He is not in the same boat as Sir Jackie Stewart, where his young, promising teammate, François Cevert, was killed while Jackie was at his best. Jackie had also lost a great friend in posthumously crowned champion, Jochen Rindt. Jackie made great progress for safety, and I think that he has a fear that another F1 driver may lose their life in the near future. Michael is apparently the driver who he deems most likely (I'd say Sato personally, but the Super Aguri can't get going that fast

). MS may injure himself before retirement from F1, but I doubt it will be even close to as bad as the injury to his leg. The safety of both the cars and the tracks is sooo much higher than that fateful day at Imola in 1994.
Relax, oh Flying Scot, Michael will know when the time is right for
him to stop racing. He does not fear the possible consequences more than he enjoys the action as you did. However, I def can't knock Sir Jackie for retiring in '73 as reigning WDC given the circustances at that time. Different stroke for different folks.
"Some people will tell you that slow is good - and it may be, on some days - but I am here to tell you that fast is better." - Hunter S. Thompson