I think the question of whether something can be forgiven at all or not is too blanket and all encompassing. Different people have different ideas about what value they attach to forgiveness and when they think it can be given. Some people find it difficult to forgive what we might think simple stuff and some do so easily for even things which in our opinion don't deserve so. Legal systems of the world also recognize this fact. For example, even after heinous crimes committed in armed conflict, genocide, civil war etc, there is setting up of Truth and Reconciliation Commissions where the focus is on getting perpetrators and victims together and seeing if they can move on. This has happened I think in South Africa, Sierra Leone and the like where murders and such have been dealt with in this manner. It is also because of this differing perception on forgiveness that people have different views on theories of punishment and crime. Looking at all this, my opinion is that whether crimes can be forgiven or not is a personal decision which can vary from person to person. I cannot begrudge people their choices. So if Swara wants to forgive Sanskaar for what he did, she can and that is her decision. I don't think his was a crime that deserves no forgiveness whatsoever and I think he has worked towards it. But then again, my opinion only.
I also don't think Lakshya has done anything completely unforgivable. He apologised for his actions and Swara has forgiven him as well. What he is doing currently is wrong again in my opinion but if and when he stops and it is shown that he is sorry and repents, I will have no problem in Swara forgiving him. But forgiving him does not equate to necessarily getting back together with him as I feel these are different things.
All of this is just my personal opinion. As i pointed out, it can vary on personal perception.