This is a very poorly worded question, because people are assuming different things.
The question made me think of bands that became more popular, continued performing after the death of members and whose later material sold better than their original material. NOT of bands that gained popularity for their original recordings, but their new lineup did not draw the same interest their original work did.
Based on my reading of the question I would have to say AC/DC is a the leading example of a band that gained popularity after the death of a member. Other examples are The Who, or the Rolling Stones.
People who mentioned Led Zeppelin and Lynard Skynard just don't make sense. Led Zeppelin broke up after Bonzo's death. Lynard Skynard still tours and releases albums, but their popularity rests almost completely on their original material. Nothing they have done since is anywhere near as popular.
Syd Barrett of Pink Floyd didn't die. He went mad. He finally died in 2006, 38 years after he left Pink Floyd.