Is there a link? Yes.
Is there a continuum between a conlang and an Endangered language? Yes. Yes.
Who should learn these languages? The descendant or any random language hobbyist?Anyone, regardless to background. Language revival requires talented hobbyists to be in the language community. Without them, the language isn’t revived, but instead a brand new creole will be created (probably an English-Algonquian croele which would be incomprehensible to any Algonquian time traveler!). Oops, I said it already, revived languages are conlangs. Endangered languages tend to be some of the hardest languages– if you only focus on getting the descendants(mostly unmotivated and not interested in languages), then where will be the talent to speak the language?
Will we be telling folk tales around a campfire? Some one will want to play ancient-life re-enactor, but most people want to translate Katy Perry in Ute. If all you have to offer is a creation tale and a song about bison, no one is going to show up at the party.
Isn’t it awful that the culture of the Utes is gone? Yes, but I can’t do much about it, certainly not when I live in Arlington, am not a hunter gather, can’t marry into the tribe (well I suppose it is possible, but it is a big thing to ask of a mere language hobbyist).
There are a few defective arguments concerning conlangs and endangered languages. Lets first discuss the typical characteristics of conlangs and endangered languages.
Conlangs are languages that invented for various reasons and studied for various reasons, usually recreationally. Conlang creators and their fans are spread out thinly across the entire globe. Most of them, Esperanto being the main exception, do not have significant in-person communities. Typically the people either have lots of spare time (high schoolers on vacation) or they are just really smart (anyone who actually can parse lojban). Most conlang enthusiasts are essentially amateur field linguists, usually polyglots, and often know how to write a dictionary and reference grammar, some even know how to promote a language and get someone to use it.
Endangered languages are mostly spoken by families at home. As the family assimilates into the host culture, they stop speaking their language. The language dies. Typically they are farmers, truck drivers, and no more likely to be a serious foreign language enthusiast than any randomly selected person. They aren’t especially likely to be conlang enthusiasts. Language revival programs are aimed at getting these people to continue speaking their language.
When the language is dead, dead, dead, down to the last speaker, then the language starts to fall on a continuum between an highly endangered/dead language and a conlang.
Virginia Algonquian. This language is dead. It exists only as a conlang constructed for a movie. The culture is dead as well. The Virginia Algonquians have all been assimilated. You could make an argument that the people with great-great-great-grandparents should learn reconstructed Algonquian, but why? Those people have completely lost the link to their language and their culture. Virginia Algonquian is now the property of humanity. And the production company that made the movie, but that is a different article.
Wampanoag This language was gone except for a translated bible. An ambitious linguist is trying to revive it in the Wampanoag community. Because fluent speakers were gone, the revived language is something of a conlang, because people are speaking a language according to what is written in reference grammars, in a limited corpus and there are no fluent speakers to tell them if they are wrong. Plus the corpus and reference grammars can’t possibly be complete. When they aren’t complete, the revivalist has to make stuff up. When the target community has stopped speaking the language and the language specification is a bit vague, you are essentially asking the descendent’s of the speakers of some language to become conlang hobbyists.
Personally, I’m not sure what my ancestors spoke. They used to speak an Afro-Asiatic language, (8000 years ago in Europe), then they spoke some Indoeuropean dialect, which changed into another language, which changed into another language, etc. My family tree is huge, ranging from SE American Indian to one each of the European countries. So, by the revivalist’s reasoning, I should study all those languages and regain my culture? Well, you could say it was a natural process, unlike the conquering of North America and the genocide and (often forced) assimilation that followed. Then by that reasoning, I should study the Afro-Asiatic language that was used in Europe before they were overrun by Pontic tribes with horses and wagons speaking PIE. But that language isn’t attested and linguists are only guessing at the family! We don’t really know a single word of the language spoken in Old Europe! So even if we wanted to revive that language, it would be entire a conlang. The PIE revival is also a conlang project.
Icelandic. Icelandic is 100% a natural language, except for prescriptive grammar. I mention it because it is a small language that is as healthy as any currently endangered language can hope to become, although with a few worry some signs. Everyone in Iceland is learning to speak English and they speak it really well. It is yet to be seen if this will lead to Icelandic going the way of Welsh, Irish, Cornish, etc. I think Icelandic is so successful in part because of the success of the domestic pop culture industry. As long as there are Icelandic movies in Icelandic, Icelandic music in Icelandic, the Icelandic language will be reasonably okay. There is even a small industry in teaching crazy foreigners to speak Icelandic. Let’s compare this with, say Ute. My point is that it is contemporary culture, and often the international extra-community culture that is going to keep a small language alive. If there was no foreign film festivals, there would be fewer Icelandic movies. If the Icelanders were speaking Icelandic just so they could retell Njals saga in the original, they’d give up on Icelandic. The Icelanders want to read crime fiction, too.
Ute. Ute is still spoken. It is still being taught to kids. It is still likely to disappear in a few hundred years. This is in part because small languages like Ute really need to have the same things that Icelandic does to survive. They need a pop culture industry– Ute books, Ute newspapers, Ute radio shows– and so on. Now Iceland manages with a population of 300,000 and phenomenal economic progress statistics. The Utes are way smaller in population and economic development. Toawac and Ignacio can’t compete with Reykjavik in terms of how people they can get to movie theaters, to buy magazines, and so on.
So how can the Utes scale up? Well, they can either have more kids and teach them Ute (and encourage those kids to become journalists, actors and so on) or they can just teach Ute to anyone who is interested. The community who studies random languages not spoken in their community (or any community that is in driving distance) is the conlang community. Alas, at best this will only add a few dozen speakers to that language. The biggest reason is that Ute is frickin’ hard. (Frickin’ hard is a technical term, which means, somewhat easier than the Caucasus Mountain languages)
Anyhow, all of those those policy decisions are out of my span of control. The reference grammar and dictionary for Ute has already been written. What we don’t have are bootleg copies of Harry Potter in Ute. A fan base, created in the same way you create a fan base for na’vi or toki pona could help move that project forward.
I for one would study Ute-lite, if there was a conference at the casinos for language learners (well maybe I can’t stand the smoke the the casinos), if there was a tengwar font, if there was a forum, if there was a online dictionary, if someone would ask politely and make a case for why I should study Ute in addition to lojban, esperanto, toki pona, Elvish, Klingon and Fursic.
Inviting the conlangers to the table won’t save the Ute way of life. The Utes in Toawac and Ignacio will stop speaking Ute and become indistinguishable from the rest of people in Colorado. I can’t help that. (Some one can! They live in Ignacio, they probably aren’t conlang hobbyists) At best, I can help preserve the Ute language as an interesting Numic language with a pronoun system unlike English that will help you stretch your brain into configurations it hasn’t been in before.
To revive a completely dead language: embrace the conlang community, embrace contemporary culture, embrace anyone who wants to speak the language.