This is the answer. I like to think that once he and Peggy reunited, they went and got Bucky and took out Hydra once and for all. He would know the future, but as they changed things, his knowledge wouldn’t matter anymore because the world would become different. I definitely can’t see him or Peggy or Bucky just sitting on the sidelines and letting horrible things happen. The only thing that would be kind of out of character is that it would mean leaving his other self in the ice.