Fair point. I guess it could have gone either way. Although Katniss does say that both her and Peeta suffer from nightmares and sometimes not being able to decipher what is reality or not. None of that went away in the books. I think in the movies they just glazed over everything. The ending was not very effective in the movies for sure, it had a much different feeling than the books.
It is hard to say how another ending would have fitted, it would be interesting to get an alternative ending for sure! Katniss completely changed her world. How everyone would function in the new world could really be anything. I think most movies would have just ended with the two heroes looking out over the destruction they left and the new freedom of the people and walked away into the sunset and left it at that.