We don't know how long the Tribble was dead. McCoy clearly states, "we need to get him into a cryotube to preserve brain function", and "you were only mostly dead". Death isn't an on/off light switch, it is a process. There was also a line, IIRC, about McCoy synthesizing a serum. He just didn't pump Khan's blood into Kirk.
We saw when McCoy was injecting the blood into the tribble. Also, since when do Tribbles have human blood? Anyway, good to see that Khan's blood also stops the radiation from Kirks body, since if it wouldn't he would die right away again. The death/revive-story seems to be a favourite of Orci/Kurtzman, they have used it in a very similar way in Tranformers 2, where they even handled it a bit better. In both cases though, they kind of fumbled it. Dying of radiation is a pretty gruesome fate. Finding a cure to that, the failing of multiple organs and brain functions at once, means you have found the wholy grail of all death cures and the fountain of youth at the same time. Yeah.
Almost seems like some folks didn't really watch the movie, they seem to just be parroting inaccurate internet chatter.
You really need to tone down the low-key insults when exchanging arguments, otherwise you will get another thread shut down really fast again.