The surviving robber would be charged with murder, robbery and conspiracy to commit robbery.The surviving robber is charged with murder under the felony murder rule which imposes liability for an unintentional homicide that occurs during the commission of a felony.  The felony here is robbery and the unintentional homicide gives rise to the felony murder rule even though the other robber was killed by the clerk and not the second robber.  The conspiracy to commit robbery is based on the two robbers acting in concert to commit the robbery.  Conspiracy to commit robbery is separate from the charge of robbery against the surviving robber.