It says here that he broke his neck, after locking up the back wheel. Given the evident lack of personal protective equipment, I'd say he got off lightly at that. But as you say, it came at the right time for him.

I think the best evidence that it actually happened is the marked change in his vocal timbre between Blonde On Blonde and John Wesley Harding.

thanks for the link and info

Interesting.

That does sound like a plausibly true account of what happened.