Oh, I see now that as soon as someone sits in Mr. Ford's seat its over. It still doesn't seem like its 50%.

Ford: 1/5 chance of last guys, 1/5 his own, 3/5 others.
Guy 2: 1/4 chance of last guys, 1/4 chance of Ford's, 1/2 chance others.
Guy 3: 1/3 chance of last guys, 1/3 chance of Ford's, 1/3 chance of guy 4.
Guy 4: 1/2 chance Ford, 1/2 chance guy 5.

But it could have ended if any of those guys sat in guy 5's seat... doesn't just depend on Guy 4.