I don't think your friend should have a problem. A quick look online said that two of the leading diaper brands in India are Pampers and Huggies, which are two of the biggest diaper brands (if not the top two!) here in the States. It would be a pain to have to pack your own diapers - depending on how long your friend is traveling for, that's a lot of diapers and a lot of suitcase space. I would just bring what I needed for the flight + 2 days extra or so (to give some time to find a store selling them!) and that to me would be plenty.