When we assume that if the Himalayas were absent, we are also assuming the Indian plate to be non existent as it is the collision of this plate with the Eurasian plate that created the mighty Himalayas. So this would mean, India will likely be a southward extension of Eurasia and instead of Himalayas there will be a vast flat land though some mountains would exist in northern Tibet ( Kunlun Shan).
So geographically, India would be exposed on all terrestrial sides. There would be no ranges in the West and North East. The subsequent huge plain in between would have very few rivers as the Himalayas were the greatest source for perennial rivers.
