It takes at least 3 minutes to fall from 40,000 feet (although a dive under power could be shorter).
That's a pretty long time.
Having said that, in 1972 at the age of 22, Vesna Vulović survived a fall from FL330 (approximately 33,000 feet, or 10km) when the aircraft (a DC-9 operated by Yugoslav airline JAT) on which she was working as a flight attendant was blown up by terrorists; She died last year, aged 66.
So it's not certain to kill you.
She had an advantage--she still had a bit of wreckage around her and she went into forest. That would tend to break her fall while protecting her against the lighter impacts from the trees. (It wouldn't save you if you came down right on the trunk or the like, though.)
The one that is most remarkable is a guy who jumped from 18,000' without a parachute. He blacked out on the way down and woke up in a snowbank. As it was wartime the incident wasn't properly investigated but it appears he hit a pine tree just right, then deep snow. He couldn't find any injuries that he attributed to the fall (he was already injured when he jumped.)
There were also some Russian experiments with using paratroopers without parachutes. The issue was whether jumping into deep snow without a chute was safer than hanging there under a chute while the enemy was shooting at you.