There are people who have tried to revive Cornish (maybe mainly in Cornwall) but I think they have to "fill in the gaps" with material from Welsh (like the dinosaurs in Jurassic Park which were recreated with the help of frog DNA).
Interesting phenomenon, this idea of trying to save dying languages. Now, I'm fascinated by language, but I just don't quite see the point of saving one that has no use.
But modern nationalism tends to promote the dominant language of a country above all others. I think it is desirable for immigrants to America to become fluent in English, but we shouldn't accelerate the disappearance of Indian languages that were spoken here pre-1607.