So supposedly.... the devil had access to all the prophecies written about Jesus, right? It was all "written aforetime" so he knew in advance the details that would help people identify the messiah. He was aware that, for the sake of God's will, Jesus would have to die.
Why didn't Satan just protect Jesus? If he's really an opposer, maybe he should've been more consistent in his opposition of god's will. If god's will was that Jesus die for mankind, why did the devil allow all of the things to happen (according to popular Christian opinion) that were predicted, including influencing Judas to betray Jesus? (Luke 22:3-6, John 13:27)
Why not ensure he lived to a ripe old age of... well, whatever a half-god's natural life span may be?