I climbed the volcanoes in Mexico when they were still "extinct"; they are very active now.
We call things "extinct" when we think they have disappeared (or in this case, inactive). It is difficult to say that something disappears. Just because you don't see it, does not mean that it is not there.
I think "extinct" is the wrong word here.
Also, what is meant by "dialects"? A little specificity would be beneficial.
Many of the dialects of German have become hidden as fewer and fewer people speak them in public. Eventually they will become lost languages.
Extinct seems to be final. We could say that Latin has died out or is extinct even though it is studied in many schools. I suspect that Stanley is looking for a word or expression in between extinct and invigorate. Eg., The German dialects are barely surviving. I'll wager that they will die off in time.