The 16th Karmapa put Sikkim behind him when he chose to pass into Parinirvana here.
There is denying this fact.
After the 16th Karmapa left Tibet he never looked back.
Why would a Karmapa take two steps forward only to turn around and reverse course?
There is no reason for a Karmapa to do so.
At least no reason that has anything to do with the dharma.