Merle's death was caused by a tractor falling on him.

http://www.angelfire.com/music5/archives/WXYZ.html#W

The niceist story I heard about Doc was when a NPR reporter was interviewing another well known singer /guitar player. I forgot who the artist was.  When asked how they got started playing the guitar they said they had a learn to play the guitar book that had some age on it. Inside the book was a telephone number you could call for help. The number was Doc's home number. The artist who was just starting out called and Doc helped him over the phone several times.