Actually Gangtok is Capital ...I was travelled in 2020 just before Lockdown... Gangtok will not be connected via Train Sevice as it is Top of the State... Rango is the Last Point where train Has to Reached. ... After Rangpo bus Ride to go to top of the Billi Area.
It is like train will never go to Top point of Himalaya..Train will reached the last point from where Hilli area started.