Corrected entry: Khan and his 72 counterparts were all a breed of the same genetic engineering. Why would McCoy remove the guy from the cryotube to keep him in a coma so Kirk's body could be saved for Khan's blood? The other 72 super humans were identical to Khan. No need to save Khan for his blood when there were 72 other donors right there in sickbay.
cadillacdude1975
14th Jul 2016
Correction: Dr. McCoy had only tested Khan's blood and he wouldn't have known if any other Augments' blood would have worked. Testing their blood would take too long, but he still needed a backup plan. But the surest way of saving Kirk was with Khan's blood. Details of this are explained in the novelization of the film, but even without this explanation, there's no plot hole. It should also be pointed out that Spock was the one who convinced Kirk not to kill Harrison, so logically he shouldn't have wanted to kill Khan, just emotionally as Kirk had wanted to.
Bishop73