It's really hard to mourn the passing of Senator Robert Byrd at age 92 (D-WV). He's nobody's favorite senator, certainly not among Democrats. He was the last vestige of conservative southern Democrats opposed to desegregation, and one of the few who didn't migrate to the Republican party after efforts to block desegregation failed. Born in North Carolina, Byrd was once a member of the KKK, a move he later claimed to regret.
The interesting question is what happens now. As Nate Silver told us "if the vacancy occurs less than two years and six months before the end of the term, the Governor [of West Virginia] appoints someone to fill the unexpired term and there is no election".
West Virginia's governor is a Democrat, so the appointment would likely be a Democrat. Unfortunately, for an appointment to happen, Byrd would have had to survive until July 3. He did not. Therefore, his replacement is thrown in to a West Virginia election.