The route from Gangtok to Nagpur spans roughly 1600 km. You will need to travel from Gangtok to NJP station or Bagdogra airport. Trains from NJP to Nagpur Junction are available, often requiring a change or a long direct haul. Flights from Bagdogra to Nagpur usually connect through Kolkata or Delhi.
Total Distance: 1600 km by road, 1200 km air distance.
Check for trains connecting through Howrah for better frequency.
Kolkata is the most convenient hub for this connection.
October to February for pleasant weather.