Prashant's character does come across as hasty and impulsive,that's for sure. It seemed to me he liked the chase,where Aarti was concerned. And once she gave in and became completely committed to him,he took her for granted. He wasnt ready to shoulder the responsibilities that marriage brings,yet he married in haste.
As for him coming back and claiming Ansh,that is a distinct possibility. There was a moment of silence,when Aarti referred to their unborn child. Maybe in future if he comes face to face with his biological child,he would want it back(esp if he doesnt have any other child). And if this happens,he wouldnt hesitate in claiming,all rights of being a father,despite deserving none. Because it is clear from yesterday's episode,that he is quite selfish,when it comes to getting his happiness,with no regards to feelings of others.