Answer by taking a quote from the following article:

Blues Traveler is an American rock band formed in Princeton, New Jersey in 1987. The band's music covers a variety of genres, including blues rock, psychedelic rock, folk rock, soul, and Southern rock. It is known for extensive use of segues in their live performances, and was considered a key part of the re-emerging jam band scene of the 1990s, spearheading the H.O.R.D.E. touring music festival. Currently, the group comprises singer and harmonica player John Popper, guitarist Chan Kinchla, drummer Brendan Hill, bassist Tad Kinchla, and keyboardist Ben Wilson.

On August 20, 1999, Bobby Sheehan was found dead in his New Orleans, Louisiana home, where he had been recording music with some friends the night before. Sheehan's death was ruled an accidental drug overdose, with cocaine, Valium, and heroin found in his system.  The remaining members of Blues Traveler convened and agreed that Sheehan would have wanted them to continue as a band. Auditions for a new bassist were held in concert, and included Chan Kinchla's younger brother Tad, who was unanimously determined to be the best choice for the role. Additionally, an open call was sent for a permanent keyboard player, a role of which Sheehan had often been a proponent. In January 2000, Ben Wilson of the jump blues band Big Dave & the Ultrasonics was chosen, and has since become a central contributor to the band's songwriting.  The band discarded their concept album material, instead releasing a smaller online EP, Decisions of the Sky: A Traveler's Tale of Sun and Storm, and went to work collectively composing a new set of songs with the new lineup. The resulting album was Bridge, which had the working title Bridge Outta Brooklyn as a tribute to Sheehan (with both the acronym B.O.B. and his nickname "Brooklyn Bobby"). The songs "Girl Inside My Head" and "Just for Me" received airplay, but the album's sales fell somewhat short of expectations.  The live album What You and I Have Been Through and the compilation Travelogue: Blues Traveler Classics were both released in 2002.

How'd he die?
an accidental drug overdose, with cocaine, Valium, and heroin found in his system.