"They were thought to be extinct in 1884 until a remnant population of eight individuals was discovered on Guadalupe Island in 1892 by a Smithsonian expedition, who promptly killed seven of the eight for their collections."
**Since that was copied from Wikipedia, the text has changed on Wikipedia, and now says "...who promptly killed several for their collections".
A lot of cultures, languages and peoples have gone extinct. There are many languages now that have too few speakers to survive, but there are also some that might survive to some extent if measures are taken to support them.
Like anything, tribes are born, develop and die.
Below are some modern day "tribe types" in a rough developmental sequence.
1) Isolated / Uncontacted tribes
These are isolated people who have a worldview that is different from any other group. They have been isolated to the point that the tribe has developed its own pre sciences or sciences, and traditions.
2) Semi Isolated / tribes that trade with other tribes, but have a unique language and defend their sovereignty
These tribes may lack adequate isolation to develop further traditions aside from defense.
Examples include tribal populations living in protected areas of some countries. France, India, Pakistan and many other countries have specific laws regarding 'their' lands that still have non colonial, non federalized people.
This would include some indigenous American tribes that speak their own language still, but most indigenous Americans are near the melting pot stage because their 'sovereignty' comes from a colonial power that has more control of their land than their tribe.
3) Melting / Tribes that are entirely defensive and disintegrating
These have entered a cycle of 'defending' a false sovereignty. They are still profitable to other groups for their wealth, but their best traditions are either destroyed or absorbed by other groups and their sciences are becoming entirely rational i.e., without art.
Examples include thousands of tribes around the world whose languages are lost but who are still trying to survive within the country that consumed them. Usually they become sort of "theme park tribes" unless they have adequate sovereignty.
This includes many indigenous American tribes. They are surviveable if they take extreme measures to restore their languages, take back enough truly sovereign land to survive, and reduce the political pressures from outside forces.
4) New Colonial Tribes / Sub Melting Pots
These are part of an original tribe, or part of a colonial tribe, that splintered off from the group from which it originated.
They may develop their own language within dozens of generations and will develop unique sciences eventually if they are isolated. Once these groups have their own language they are more survivable.
Examples might be Taiwan from China, the U.S. from Britain, etc.
5) Old Colonial Tribes
These have their own language, a body of traditions, and consider themselves homogenous. If they had adequate space they would start evolving again soon, like isolated tribes.
Examples include the Amish.
These are either brand new "tribes" deliberately created with a specific motive, or a collection of people from other groups who are trying to synthesize a national or tribal identity.
6) Traditional Frankenstein Tribes
Are an attempt to revive a language and legitimate tribe that is extinct.
Examples include Israel and other "new" old tribes built around reviving an extinct language. This would be the closest parallel to most indigenous American tribes whose languages are completely lost.
These groups do not survive as tribes unless they are isolated. The more the original traditions revive, the more physical space is necessary, and the less isolation/space, the less they develop.
Native tribes in North America are given land 'reservations', but always with the clear understanding that their patron is the conquering federal government, who can take their land at will. Native Americans, like most captive tribes, are prevented from defending themselves.
7) 'Lord of the Flies' Frankenstein Tribes are non ethnic gangs that develop a culture and set of traditions.
These can be semi corporate groups, "castes" etc. or groups like "the rainbow tribe" who try to create an identity out of t shirt mottos.
8) Corporate Frankenstein Monsanto Tribes.
These are ‘Lord of the Flies’ tribes which are deliberately formed by individuals for profit of some kind, and have no basis in real tribal identity. They form arbitrary boundaries depending on their military capabilities. The United States is probably the closest to this kind of tribe.
The result is a confused mass of rootless people living within artificial boundaries. The premise of the founders is that at some point a real ‘ethnicity’ will develop. It’s an imitation of how real ethnic states formed, but thousands of years too late. It can be propped up for a while, but ultimately will not last.
When space travel begins, within the next few decades, it will depend on real diversity to succeed. Having a mass of homogenized people who have been stripped of their long term identities, and who pretend diversity, will be the signature of failed space programs.
Groups that have their own power, including language and currency, and which operate independently of any control will eventually have all of the power. Trying to falsely federalize each group or tribe so they are like domestic pets of some self appointed "leader" group will be an obvious fail.