Agreed with you mate, there is lot of difference between Tibet and Sikkim. I just want to clarify that, India will not support for the independence of Tibet as the situation has been changed now. If they do so, china will counter back with the support for independence of Sikkim and Kashmir.
There is a big difference between Sikkim and Tibet. The people of Sikkim don't want to be independent. The state is having a Hindu majority, and they are happy being a part of India. But that is not the case with Tibet. Even now, there is a lot of support for independence there. And talking about Kashmir, it is true that the majority of the population want to secede from India.