Did Jesus really die on the cross?

Yes — that Jesus was executed by crucifixion is one of the most secure facts about him, granted even by sceptical historians who accept little else in the Gospels. The 'swoon' or apparent-death theory does not actually dispute the crucifixion; it disputes that the cross killed him, claiming instead that he only fainted, revived in the cool of the tomb, and slipped away. So the real question is a narrow one: did the crucifixion end his life?

The medical evidence points hard against survival. The most-cited study, published in the Journal of the American Medical Association by three Mayo Clinic authors, William D. Edwards, Wesley J. Gabel, and Floyd E. Hosmer ('On the Physical Death of Jesus Christ,' JAMA 255, no. 11 [1986]: 1455-1463), concluded that Jesus most probably died of hypovolemic shock and exhaustion asphyxia, and read the spear thrust and its 'blood and water' (John 19:34) as consistent with fluid that had gathered around the lungs and heart. This is a careful medical interpretation, not a proof — the exact physiology behind the 'blood and water' is still debated among the medical papers themselves, so it is best held as 'probably,' not pressed further than the evidence allows. Surveying the modern medical writing on the question, Gary Habermas, Jonathan Kopel, and Benjamin C. F. Shaw ('Medical views on the death by crucifixion of Jesus Christ,' Baylor University Medical Center Proceedings 34, no. 6 [2021]: 748-752) find broad agreement on the modest, uncontested point that a fully crucified victim does not walk away alive. There is also a concrete historical case, not only a medical model: Josephus records that when he found three of his own acquaintances among a group being crucified during the siege of Jerusalem, he begged the Roman commander Titus for their release and had them taken down and given the best available care — and even so, two of the three still died (Josephus, The Life 420-421). If even men deliberately rescued in mid-crucifixion and tended by physicians could not reliably be saved — two of those three still died — a Jesus who was scourged, crucified, speared in the side, and sealed in a tomb with no rescue and no care was in no condition to quietly revive on his own.

But the theory's deepest failure is not medical; it is historical and psychological, and it was pressed by a hostile witness. David Friedrich Strauss — no friend of Christianity — argued in his later work A New Life of Jesus (1879), a separate book from his famous 1835 Life of Jesus, that a man half-dead from crucifixion, who had crept from the sepulchre needing bandaging and care, could never have persuaded his disciples that he was the risen 'Prince of Life' who had conquered death. Such a battered survivor would have sent them for a physician, not into worship. So even granting, for argument's sake, that Jesus had somehow lived, the swoon theory still cannot explain what actually needs explaining: the disciples' conviction that they had met the risen Lord.

On both counts, then, Jesus really died. The apparent-death theory fails on the medical evidence and fails again on the psychological evidence, which is why it has almost no scholarly standing today. To go deeper — including how the burial itself served as the authorities' public sign-off that Jesus was dead — see the linked study.