Just to put an end story to this for those that helped. He arrived to discover the BOM-CCU flight was delayed by 2 hours, making a connection possible (he'd arrived 5 minutes before it was due to depart).

Sadly it took 2 hours for the baggage handlers to deliver the luggage - his was marked priority. Apparently 6 priority bags came out within minutes, but then the luggage belts stopped for 2 hours. Oh, there was an a/c (or heating) problem, other flights had been cancelled and all hell was kicking loose ensued

As a result there was 2 hour wait to get rebooked - he took it upon himself to go from the ticket desk to the main Air India office where a few people were sitting around doing nothing! They confirmed he was booked on the flight 12 hours later, and wouldn't rebook him on another airline, so he walked upto the Vistana desk, booked himself for 7000rp on a flight in an hour, and arrived in CCU only 5 hours late. His next job is ensuring his return flight is protected. Under normal circumstances i'm sure it would be cancelled but with Air India..