Well, if the Senator was incapacitated, maybe there might be some debate.
But when the Senator is dead, the seat is as vacant as it can get.
West Virginia law fails, however, to state exactly when a vacancy occurs. Whether the vacancy is considered to have been created at the moment of Byrd’s death, when the Senate informs state officials of the vacancy, or when Manchin declares the seat vacant will be crucial.
Depends on the definition of “dead”...................