It think it's coming. Then again, who knows, Hemsworth may want to keep doing the character. I think Captain America is gone, we'll see him replaced by either Sam or Bucky (My money is on Sam, everyone is referring to Bucky as "white wolf" that'll be the direction they go with him.
http://comicbook.com/marvel/2018/02/...-bucky-marvel/
I doubt RDJ will keep playing Iron Man, but who knows. I think Avengers 4 will see several old heroes sacrificing themselves to give the new generation of heroes their lives back.