I don't think it's going away, since breaking oaths is an important part of playing as a Paladin in 5e. And the concept of Fallen Paladin is old, very old. Even BG1/BG2 had it.
I didn't mean all oathbreaking, but maybe oathbreaking will be streamlined down to clear "this is an oathbreaking situation" dialogue screen, or a blanket "no killing yellow dots" rule will manifest, or (the better option, in my opinion), paladins will come with a Paladining 101 manual so that for the player's it's crystal clear what they can and cannot do -- or at least as clear as it would be for their characters.
