And the answers are...

"Gangdom's Doom" was Claude Fellows' final appearance in the pulps.  He was gunned down in Chicago while on assignment for The Shadow.  After witnessing an execution by the mob Fellows' days were numbered.  He was slain by Machine-Gun McGinnis in a drive-by shooting.  McGinnis was captured and later sentenced to death.  Small comfort to The Shadow and the other agents who knew Claude, but that was a risk that all who serve The Shadow willingly take.