This show is a beautiful portrayal of human emotions. It teaches us how one's decisions has an aftereffect on others and also on oneself.
I am 100% confident that Dev and Sona will unite in the end as only through that makers can convey a strong positive message that - It is ok to make mistakes but once realized one should work towards correcting the damage done and apologize. How one should not let ego come between relationships, have a big heart and forgive when you see someone genuinely repenting - be it Dev or Ishwari.
If Dev and Sona do not unite, only negativity will be spread as the makers will be trying to convey the message that see how one mistake leads to total disaster and so one should try becoming God and never make mistakes and if you do..see the consequences. You can never rectify mistakes.