The past plot points in Cap by ED were all there. As to why Red Skull didn't just kill him simple Skull doesn't just want to kill cap he wants to break him as in break his spirt and soul and belif in America. I think he planned to do this to cap bring him back and have Zola age up caps kid and transfer skulls mind into it and then destroy america while cap watches and have him do it in the body of cap's kid. This would break caps spirt and belif in america then skull kills him. As to what he did I wonder if the gun sucked out Cap's soul aka lifeforce and shot it through time. and maybe sharon wasn't the constant maybe the baby inside was being part steves. I wonder if sucking out the life force aka soul is what made the body shrivel up like that sort of like gentleman ghost did in an epsoide of batman brave and the bold AND NOT THE SUPER SERUM LEAVING THE BODY.. The body would be perserved at the bottom of the artic in the cold and when the soul is returned his body will go back to normal.