What was Indian food like before the arrival of the chili pepper from the Americas?
Hardly - pepper was exported from India before chillis were introduced. Some linguistic subgroups still use it in preference to chillis, and certain dishes use it in preference to (or in addition to) chillies.

Ginger's also native (or at least an early import) to India (and while not always used in 'traditional' cooking), I do believe that garlic and ginger were as well.

Many other spices - one of the cinnamon varieties, cardamom and quite a few other spices were native. 

While fairly well known, chillis aren't essential to cooking.

Oddly enough, the 'source' I used to try to reverse engineer what are 'native' and what aren't is the traditional funeral anniversary or 'thevasam' menu. While essentially vegetarian, it would use mostly native produce and spices. You can find an example here, though specifics tend to differ with cultural groups or even families