I doubt it
I doubt that Toshiro is dead. Giselle only needs to kil quincies to zombify them. Shingamis don't need to be dead. His appearance leaves some questions but I think it can be explained. It is likely that the longer as a zombie you are, the more zombie like you appear. I really doubt that he died after fighting cang du and I really doubt Giselle would have killed him because she didn't need to. HE is probably severely injured and will be more in this fight, but I think he will pull through. I don't see any need for his death and I don't see Kubo writing his death, he appears to like Toshiro as a character too much to die. He will stick around.