While it's historically possible Lauder was very badly burned and DNF one race and didn't even take part in the next 2. Something like that isn't remotely likely these days.
As I said above, it is unlikely but not out of this world. See what happened to Massa in '09.
I think the odds you'll get on a Vettel win at the moment (~1/14) reflect the chance of him being involved in an accident that takes him out of the picture for a few races. It's very hard to see anyone else beating him in a straight fight, even if McLaren or Ferrari did manage to find a second a lap on the Red Bull for the second half of the season, Button/Hamilton/Webber would be taking points from each other and Vettel would still regularly be finishing with half decent points.
The season is Vettel's unless he's forced to sit out a few races due to injury or experiences a string of freak mechanicals or collisions.