Did Scarecrow Really Die?

During Batman Arkham Asylum Batman chases Scarcrow down into the sewers and killer croc comes and and grabs Scarecrow then dives back into the water. That is the last we see of Scarecrow. Also during an alternate ending of Batman Arkam Asylum we can see scarecrow climb up a Titan box in the river. During Arkham City There is an easter egg of  Scarecrows mask on the ground. ( Riddle: If your scared, dont be afraid to crow about it) Also there is fear gas containers in varios parts of the city. And there are strange radio transmissions that are belived to be from Scarecrow that say revenge plans like City of Fear. But yet we have not seen any physical apearance of the Scarecrow since the inccident
 with  Killer Croc back at the asylum.