A believer might be content to take the Bible's word for it, but a historian has to consider the evidence.
McGrath points out that it was possible to survive crucifixion. He writes of the Jewish historian Josephus,
At one point he came across some of his friends who had been captured by the Romans and were in the process of being crucified. He petitioned for them to be taken down from their crosses, and one of them managed to survive (Life of Flavius Josephus 75.420-421). It was therefore possible to survive crucifixion at least in cases where the crucified individual was taken down relatively quickly from the cross.He says that others have suggested that the vinegar given to Jesus might have been a drug meant to knock Jesus out, making it look like he was dead, so that he might be taken down and later revived. In addition, he says, the story of the Roman soldier piercing Jesus's side might have been created to counter the claim that Jesus didn't actually die.
McGrath points out, though, that "the Romans were quite adept at execution, and it seems unlikely that friends of Jesus would have been able to give him a drug to cause him to appear dead, thereby outwitting the Romans." If that was even possible, it probably would have been tried numerous times, and there would be some mention of it in texts from that era.
Furthermore, he says, "Jesus’ followers were willing to give their lives in later years for their conviction that Jesus had not simply survived death, but had been raised from death and seated at God’s right hand." That they were willing to die for this belief doesn't mean the belief was correct, but it strongly suggests they actually believed it. And they didn't just believe it, they made it a central part of their message. This, he points out, is "crucially important" evidence:
Most people in that time would have assumed that crucifixion by the Romans was a clear indication that someone was not the Davidic Messiah. It is the closest thing one can imagine to an automatic disqualification. Had Jesus survived the Romans’ attempt to execute him, that would surely have become a centerpiece of Christian proclamation.The Burial of Jesus is a good read (and a short one, too; I downloaded it the other day and was finished in less than an hour and a half). I do recommend it.