Although seemingly different, these two ideas stem from the same viewpoint: Were it not for the Chinese occupation of Tibet, Tibet would have remained isolated. Nothing would have ever changed.
Before I begin my rant, I want to note that it is impossible to know what truly would have happened had the occupation never occurred. The best we can make are educated guesses.
That said, I think this view point is completely false. Why on earth should we assume that nothing would change over the course of 50-plus years? Tibet was already on the brink of change when the occupation started. The young Dalai Lama, rapidly approaching majority (the age at which he would take full political power), was interested in contacting the outside world. He wanted to bring democracy to his country. He had frequent contact with some of the foreigners residing in Lhasa, petitioned to statesmen abroad and had a great interest in the world outside of Tibet. It is safe to assume that, had Tibet retained independence and the Dalai Lama been allowed to attain majority as head of the Tibetan government, he would have pushed for a more open, democratic Tibet. In fact, when the Dalai Lama did attain majority and move the Tibetan government, one of his first moves was to declare the Tibetan National Government the only valid government of the people of Tibet and that this government was now a democracy.
In addition, with the British invasion of Tibet in 1911, the Chinese (even before the communist party) invading and encroaching on numerous areas of Eastern Tibet, the Russians sending in spies, India gaining independence and virtually every neighboring country shifting governments, it is unimaginable that Tibet would have been able to retain isolation.
Let's look at other countries. Prior to the mid 20th century, many countries around the world were in semi or complete isolation. For some, the isolation was due to a political choice, but for many others it was due to location or a lack of technology. Honestly, how many of these countries remain isolated now, in the 21st century? Even North Korea, the most self isolated, totalitarian and closed country in the world, has advanced technologically by leaps and bounds in the past 50 years. Remember, North Korea, unlike Tibet, is a country that desperately wants to remain isolated and is perfectly happy to oppress its own people.
How can we reasonably believe that Tibet would have remained the one exception in the entire world? The one country that, as all nations were swept forward in the technological and communication advances of the 20th century, would have remained stagnant in time? To believe that is to believe that Tibetans were too backwards to look towards the future.
As for the Buddhism comments, prior to 1959, the Dalai Lama had already travelled abroad to India at the invitation of the Indian government to go on pilgrimage and to celebrate the Buddha's birthday. He knew that there were Buddhists all over the world and many great masters of the past had travelled widely. I am sure that someone with as much drive as he had at such a young age, and still has at the age of 76, would have made every effort to travel abroad. Tibetan Buddhism, which had already been partially disseminated in the rest of the world prior to 1959, would have continued its spread when the Dalai Lama travelled. To believe that he would have been content to reside in the Potala for the rest of his life pays no attention to the kind of young man he was even before the Chinese ever came.
Cultures like Tibet are not quaint showcases in museums, perpetually remaining in one moment in time for others to ponder and exoticize. All cultures, Tibet included, live, change and grow. To assume otherwise is to disempower the people of those cultures.