I do not recall much and cannot pin point the issues, but didn't Baron Zemo make an offer to Captain America for his help. Something about he can't win, without him. And I don't think that ever really got resolved and I have no idea where Baron Zemo went to.
But if there is a person who could outwit everybody on the stage of an actual death, Zemo is certainly a top ranker. Zemo also wanted to prove himself and I think there was mystical forces saying he would redeem himself in the future. But then he's gone, Thunderbolts moved on and Captain America is dead.
I won't give DC all the credit for thinking ahead and having complex storylines set up months even years before they go down in a big way from a little trickle, but Zemo, Red Skull and Captain America And all the rest of that 60's/70's era stuff that and eveything going on in Captain America it is certain Steve Rogers is dead. Everybody speculating on when he will be back and how, so I am tossing my 2 cents in and with some hlpe on people who know what happened to Zemo..
.. that Baron Zemo is the one who brings Captain America back and had already started weeks before his death actually happened.