Most airlines in India have very good records in these matter.. here are the things you need to consider:

1. If you are flying a LCC (Spice OR Indigo) and in the off chance they do cancel their flight, they might be more inclined to offer you a refund than book on another flight with the same airline, or another airline..

2. If you book with a FSC (AI or Jet, or Jet Konnect also)- they would make some amount of effort to book you on another flight rather than give you a refund.. the reason I include Jet Konnect here, even though they are an LCC, is because, they belong to the Jet Group, so if you tell them that you have an international connection, they will be more accommodating..

3. And lastly- but the most important point - Flights do get cancelled in India, just like any where else. Even though they do mostly have good record, but flights do get cancelled.. you bigger worry should not be that whether you would rebooked or a refund.. you actual worry should be, if you are flying an off sector like Varanasi -Del, and your flight gets cancelled, and there is no flight to Del after your flight, even if the airlines rebooks you, that might make you miss ur international connection.. so you might want to consider returning to Delhi a day in advance, to factor in such a scenario.. or don't book the last flight out of any city, to allow yourself the option of switching flights at the last minute..