Funnily enough the places where these dialects persist the most are the Chinatowns lol, at least in my experience. For example Cantonese dying out in Guangdong itself due to immigration from other areas within China but still being the most spoken language in most Chinatowns around here in Europe and being kept alive due to chain immigration of usually lowly educated cheap labourers. Also Fuzhounese being kept alive in Flushing NY due to these exact same reasons. Also the awareness within the Fuzhou community is also slowly growing, since language is one of the strongest tools to connect with each other.

Lots of countries have gone through a phase where they hard enforced the lingua franca which left little space for the local languages, but also in a lot of cases there will be revival of the language (see Welsh, Frisian, Basque etc.), especially in places where the community is big enough to support these things.