These statements, coming from you, are very disappointing.
Firstly, it's unclear if the people of IVC practiced monotheism or Animism involving multiple Gods. There are figurines of both Mother Goddesses and Male Deities recovered from IVC. That makes it at least two Gods right there! How were they monotheists then?
If the Aryans entered India around 1500B.C and dominated the land that constitute Pakistan, then the people of IVC must have adopted Hinduism at least from 1200BC to 200BC, till Buddhism arrived, spread by Ashoka. A lot of classical Sanskrit authors came from the region of today's Punjab and their texts make it clear that Sanatana Dharma was the only major religion in the area. Buddhism too, was not spread only in today's Pakistan but in large parts of India at it's zenith. This was mostly from around 2nd century BC to 4th Century AD, before the Gupta empire revived Hinduism. The first conquest of Moh'd Bin Qasim on Sindh took place in 8th century, but it wasn't at least until 12th Century that Islam found a political foothold in India and mass conversions to Islam took place in Punjab and elsewhere. Islam and Hinduism were spread in every village of every province of India by the time the British took over. The stats speak for themselves. Lahore had an equal number of Muslims vs Hindu-Sikh combination at the stroke of independence. Weren't the Hindus+Sikhs of Lahore the same descendents of the people of IVC? This was pretty much the case throughout Punjab and Sindh (very very few districts had 2/3rd Muslim majority in either of these two states).
I am sorry if you are disappointed but what I am stating is factual in entirety. You say that there were figurines of Mother Goddess and male Deities recovered from IVC. These figurines became Goddess and Deities because thousands of years later these were identified as such by a religion in India and not because the people of IVC also accepted and characterized these as such. This is justification in reverse and does not prove anything.
The Aryan Invasion Theory has been debunked a long time ago and I do not agree with any such happening taking place. If at all there were any migrations that took place, these would have been over a long long period of time and would not have changed or impacted the local culture in a big way. The fact that the people of IVC conducted major trade with Mesopotamia, yet also the fact that no Mesopotamian cultural similarity exists between the two civilizations speak of the strength of IVC civilization in maintaining their societal and cultural singularity and distinctive and separate identity. In such an environment, how could the invading and migrating Aryans would have changed the cultural and societal practices of the people of IVC - they could not have.
Most of the Vedic period falls within the early part of the Iron Age between 12th to 6th centuries BC. This was the evolutionary period and one can not state this with any surety that whether the people of IVC followed Vedic culture. You see even after complete fading out of IVC by around 1300 BC, the people living in the cities did not move out of these cities and continued living there and this has been accepted by all the archeologists and historians that I have read. The Vedic culture as described in the Rig Veda is primarily rural in nature and the IVC people even after complete fading out were still urbanized in nature. This change, if at all, would have occurred much later in time frame and could not have started around 1200 BC. Talageri describes the emanation of Aryaverta as not Punjab but area east of Punjab and he says that it later moved west to Punjab. Which would also place it much later in time frame.
And if these people followed monotheistic format, as many scholars believe, their religious format would certainly be different than the one Indian Hindus practice. Many scholars believe that Porus, who fought Alexander the Great around 300 some BC, was a monotheist and thus falls well within the expanding history. Kushans invaded in the 3rd century BC. Various Kushan emperors represented a wide variety of faiths including Zoroastrianism, Buddhism, and possibly Shaivism (monotheists).
In pre-1947, non-Muslim population in present day Pakistan was:
1. W. Punjab: 9% Hindu, 11% Sikh
2. Sindh: 10% Hindu, 5% Sikh
3. NWFP: 2.5% Hindu, 2.5% Sikh
4. Baluchistan: 3% Hindu
According to the UN and other respected organizations, 12-24 millionis the total estimate of migrations from both India and Pakistan(East Pakistan included) of Muslims, Hindus and Sikhs combined at the time of partition. This amounts to almost 50% of the total Hindu and Sikh population migrating to India.
Therefore, the history very clearly indicates that since the earliest times, there was never a majority Hindu population in the areas of Pakistan.