Considering how much time Aamir will take to make another movie, there would be no impact.
JHMS also was released 1.5yrs before Zero, compared to TB and Ra.One which released a few months before Don 2 and TZH.
So the impact might it might not be there. One big advantage here is that so few people even know of the movie and so few have seen it that there might not be much negative impact. I mean majority viewers were diehard SRKians who will show up next time regardless. I guess having the same heroine with another romance movie could backfire, we'll find out on 21st Dec.
As for Bharat, too early to discuss that.