Gpay with foreign CCs in India works spotty at best. The moment your phone notices that you are in India the Gpay app changes from the EU/US version to the Indian version. The first time I noticed this was during my trip in September 22: the icon and text of my app went from a logo of a few cards and a title 'wallet' changed to 'Gpay'. I managed to pay once using my German card when my physical HDFC Rupay card was not working. Since I don't use my foreign cards in India and try to use the Rupay card where ever possible it was not a major hassle.

Regarding cash and how to dispose it: note that foreigners are technically not allowed to take INR currency notes/bills out of the country. Of course thats not really feasible and no one cares. I try to use it up as much as possible, the easiest is to pay the hotel with whatever cash you have left (hotels can always settle the payment with a mix of credit card & cash) and just keep a small amount for the taxi to the airport.