Eddy Shaver...without a doubt! Eddy had been making incredible music, for years, with his dad, Billy Joe (not to mention others like Dwight Yoakam, Todd Snider, Guy Clark, Willie & Waylon). But when he passed Eddy had just inked a deal with Antone's and was getting ready to spread his wings and fly.
My choice would be Lowell George of Little Feat. The band is still very good but hasn't been the same since Lowell passed. What a great author, musician & artist.