Nowadays, mostly because of globalization, people tend to learn the most used languages to be able to speak in almost every country when they travel. There is an higher probability for this to happen when the spoken idiom is used by regions with a population of no more then hundreds of people. Of course, on long term this can cause losing their native language.
I believe that there are different scenarios of this possible situation, for example there are so much idioms in Italy other than Italian and people in Florence, Turin or Naples use languages that are not understandable by someone not native; but, I don’t think that this kind of idioms will ever be lost because somehow they will always be handed down to new generations. So, in this case I don’t think there is need from governement to protect it, because it is already done by population itself.
On the other hand, this might happen with idioms that are not written in any kind of book and they are only spoken by older people; so, in this case, can be hard to not lose it. In fact, this situation is currently happening in some regions around the world. In addition, there could be another type of scenario where people that come from regions that are situatued close to borders speaks older idioms. In this case could happen the situation referred in the first paragraph. So, in both situations, there is need to protect it by legal means from governement or it could lead to lose it, even if in the first case it could be difficult to achieve that.
In conclusion, I think that there are so many cases of minority idioms that we need to consider where protect it is actually needed. Also, we need to think that in history so many languages evolved and I don’t think this could be considered a bad thing.