Cantonese will not be endangered for a very long time. Even in China mainland, its status is right behind Mandarin. There are a lot of arts I.e. music, movies, TV that heavily focus on Cantonese from Canton province and Hong Kong. Some award shows in Canton (and obviously Hong Kong) have separate categories for Cantonese and Mandarin. Thus as long these forms of media is popular on the internet and popular culture, the language will continue to flourish. Furthermore given that Hong Kong and Macau are special areas where the government has minimal interference, and thus doesn't force them to prioritize Mandarin to replace Cantonese.
Those are the main difference between Cantonese and other minority dialects within China. Another huge difference is the prevalence, heritage, and influence of Cantonese outside of China. That is, Cantonese is heavily spoken in many places around the world, which cannot be said of other dialects. In Southeast Asia, Cantonese songs and shows are quite popular and often get played on Chinese stations and categorized in awards shows alongside Mandarin. USA and Canada have huge Cantonese speaking populations. Even Europe and Australia where not as many Chinese reside as in America, nevertheless they do have tight-knit communities that continue to speak Cantonese.
That's one of the underlooked, underestimated factors of Cantonese: survivability and momentum. Many communities outside Asia where Chinese people settle have Chinese schools, and the most common dialects taught are Mandarin and Cantonese. So children will continue to know how to speak, read, and write Cantonese. Furthermore the popularity of Cantonese movies, songs, and TV shows are played worldwide. Mostly thanks to TVB (the biggest TV station in Hong Kong) which can be subscribed in USA, Canada, Singapore, Malaysia, and other parts of the world. So Chinese people can watch high quality Cantonese shows everyday.
As for other dialects beside Cantonese, I don't know their situations. It's up to the natives how much they want to keep their language alive. A language's longevity is not just how many speakers, but also its contribution to arts, culture, education, economy, etc. Cantonese speakers are very passionate and creative about their language, and that shows in their movies, songs, and writing. Since I was raised in USA and learned both Cantonese and English from very young, I think Cantonese is a lot cooler, funnier language. I much more enjoy Cantonese movies, songs, humor, and poetry than English.
Speakers of other languages must have that same level of pride and loyalty to maintain their language. They have to spread their language through various means; no one else can do it for them. They have to make arts and schools to raise awareness of their language's importance. No one else can do it for them. When Chinese settled in foreign lands, nobody asked them to set up Chinese schools. They did it on their own because they feel it's important to maintain and conserve their language and culture. Very few people in the world really care about whether a language dies or not. Chinese government does care somewhat, but they can't do everything. It's up to natives to do the heavy lifting.
(Originally posted at http://www.omniglot.com/forum/viewtopic.php?f=14&t=1107)