He was quite dead hours before the ambulance arrived. Most assuredly. This is very quick and gives no warning, unless a prior arteriogram of the aorta and sub aorta shows the beginning potential areas of separation of the innermost endothelium from the outer layers/smooth muscle of the aortic artery which heads down to bifurcation to the two kidneys and thence to the major femoral arteries to the legs and offshoots to the abdominal organs.
Very short, likely terribly painful then— lights out. Remotely possible aggravated by blood pressure issues and long pressurized air flight— has been posited clinically in the past.
If the Aorta tore, it would be like a pipe blowing in a closed heating system. The pressure would drop dramatically in a second. He would have been unconscious in a few seconds. He might have felt something but he would not have comprehended what was happening.