I want to jump in on this one.
I personally don't think Gin died. I mentioned in another thread that i thought he was the perfect double agent and he was a snake. When a soul reaper dies, their Zanpakuto breaks down. We saw that with several characters, like Byakuya. he definitely was supposed to have died, though he is a coma. I believe Gin set out on his own just like he said during his final encounters with Aizen and this is where i think he FAKED his death. Its the only thing for an Assassin or double agent to do to perfect his skill and abilities and remain hidden. This makes me believe Aizen and him were in on it together to awaken Ichigo from the start because of the upcoming battle. I think Aizen knew something.
We never actually see Gin die, get a burial or ceremony like most main or important story characters. In the anime sure we see a limp hand. He told Rangiku a bunch of secrets. most of what we got to watch was a love story flash-back. Seriously i would think someone would be given honors or a ceremony of some sort for defecting as a double agent/assassin. He did it the right way, everyone thought he was the bad guy the whole time.
Though there really is no doubt at this point the revived Character(s) is definitely Grimmjow at this point along with half of Xcution