Yes, i completely agree with you. It would had end up like this

1. She would have got married for real and than after a year she got a baby.
2. And after a year , as the hero passes through the street he would have seen priti sitting in park with the baby in womb .
3. Then he should have realize that he should move on with his life because he is not made for her .
4. This should be how the beautiful love story should have an end ,with a meaningful message to the couple.

But yes the movie has a twist in the end!!

The best part i liked is, both of them suffered a lot to get back together like, while Shahid was killing himself with alcohol, Kiara was suffering through pregnancy. He vomits, she was vomiting. He lost weight, she gained. He is thrown out of his house, she was thrown out of her house. He found a job, she found a job. He had one faithful support (his friend), she had one faithful support (the old woman in her lodgings who cared for her). They were the same, beginning to end, and both their hurts were doubled because they were feeling the hurt of the other.

The point of the film is to trust your partner, to believe in yourself. Shahid knows, for the whole movie, that he is meant to be with Kiara.