If Yash was not at fault, people like Zoya would stay single with the memories.
And coming to Adi, he will have no come back. His wife cheating on him with his brother will devastate him enough to become normal.
Yash and Pooja having affair is the best way the makers can progress to explore more angles in both Zo and Adi.
I know writers are different but ths production house plays weird mind games! In Beyhadh, when Ashwin was killed they tried to make viewers believe Maya, Arjun, Mayas mom, Vandana etc could have murdered him. They didn't go out of the way and showed Maya killing Ashwin as expected.
So I would not really be surprised if they keep the affair of Yash and Pooja as the final conclusion.