In my opinion this history can be additional to the two nation theory....even if our ancestors did not convert to Islam, coterminous Pakistan was still different....it was only the colonial entity known as British India which made "us" the same....
I don't read too much into it. Because Muslims have more to introspect about themselves and their Islamic traditions and there is conflict of ideas between right way of following Islam.
I have no idea old ruins but what I know that those who were Muslims in Pakistan remained in Pakistan and those who were not they left as they were more comfortable with the otherside.