I also have concerns for this trip.
The destination is not the most female friendly, safety is a huge factor too
Depending on the family's financial situation, they could be more or less westernized - home facilities speaking - toilet, ac, etc.
People may look at you and become fixated at you in public, if you are not of indian descendant.
Do you speak urdu or hindi?
Moreover, where does he live? With family, on his own?
Guests are supposed to be very respected according to their religion but we all know religions are not always followed as written and cherry picked as it may be convenient
What is the purpose of the visit? It makes me suspicious, given that his wife passed away recently
I would go to another location, bring a friend and enjoy the visit with your long term friend.
I have been to India and culture shock was huge. Never felt so alien before.
It was like a bulb pointing at me - look, a white woman! - and people would stare forever, so much that my indian ILs would tell them to stop
Food will be a huge challenge too.