With the new game plus mode now added, which is fantastic, the Walk Away ending is now completely useless. It doesn't actually end the game, it just reloads back to Hope County as if the ending didn't happen and the Final Confrontation mission is still here. New Game Plus isn't rewarded. So... The game essentially tells you to "go back and do it properly". Why can't both endings be equally final? I prefer the Walk Away ending and I wish I could choose it and actually finish the game instead of just kicking me back to do it again "but properly this time".
The walk away ending can also be found at the beginning of the game if you stand there for long enough without taking action against Joseph Seed. This doesn't seem to be a technical issue, and I recommend that you make a feedback thread about this issue if it's something you would like to see changed.