So, we slowly forgot our own language (the other parts of the country that were not dominated by the English to such a degree, actually look down on us a little bit, because we do not speak Welsh as our main dialect...).
Recently due to pushes from the government, more and more children are growing up and learning welsh, and it's now at the point that most jobs in wales are successfully requiring Welsh-speakers as part of their hiring.
It's completely possible to resurrect a dead language with native language speakers still in existence, it's faster than killing the language (It took 300 years to completely eradicate Welsh and only about 50 years of government efforts to resurrect it), it just requires the collective will to be there, and the wish to restore the culture (or some bastardized idealized version of it).