Jackie Wilson was buried in an unmarked grave that didn't get a headstone until four years after his death.
Any others in this category? IIRC, Frankie Lymon ended up in an unmarked grave, and even after a fan raised the cash to buy one and have it inscribe, because of squabbling among his widows (seems Lymon didn't believe in divorce before remarriage) it hasn't been placed.
Here's a Lymon video.
Twelve years after this was recorded, Lymon was dead of a heroin overdose.
In both cases, I think it's safe to say the musicians are respected by fans today, but at the time they shuffled off this mortal coil...not so much.