People that left because of the NTR aren't likely to come back, even if there is a promise of no more NTR in the game. The fact that it exists in the game at all is enough, even if they got through the scene and that's the end of it. For them, the game dynamic and the relationships have been forever altered in a way they don't like. It's like if they kill off one of your favorite characters in a tv show, then they promise not to kill anyone else afterward. Well, that's fine for the other characters, but the one you liked is dead. Can't change that, or if you do it still won't undo the "damage". I don't even think going back and making the content optional or removing it entirely would help much either. Some wouldn't trust the dev after that, and while you can physically change what happens in the game, you can't change people's knowledge of how it originally played out.
As for new people, the ones that don't like NTR would probably avoid it instantly because of that tag. Others may ask here if the NTR is avoidable or for more info on it, but once they get their answers they'll probably nope out of playing the game.
Are there a huge number of people in either case? I can't say. Obviously many have spoken up against the last update, but people rarely speak up unless they have a complaint. Maybe it will have a noticeable financial impact on the dev, or maybe not. Maybe any loss will be offset by pro-NTR people supporting the game, although in that case they'll likely push for even more NTR. That seems to be the trend. Some regular fans leave, NTR fans fill the gap, but the dev gets pressure to add more NTR content, whereas up to that point people were content to let the story they expected from the dev to play out.
