Yes, he could have healed His body, but then we would still be in our sins and eternally lost. He suffered a literal physical death, which He allowed, ergo, no man takes my life from me. By the way, it was necessary for the Lord to suffer a physical literal death, because the reward for sin is death. But because He himself had no sin He therefore did not owe the debt. By making the payment, He represented us as a human being and His payment is credited to everyone who would have faith in Him, so that though we die, yet shall we live. Since the payment has already been made, then those who believe no longer owe that debt, because it has already been satisfied by the Lord.