So if state law doesn't apply on Reservations that actually opens up all sorts of questions, like take driver's licenses, those are issued by the state, so how would people on a Reservation get one? My parents definitely had North Dakota ones while on Standing Rock. Does a suspended license mean you can still drive in one? And what determines penalties for crimes, if you kill someone on a Reservation are you actually charged under some tribal statute for murder instead of the state one?
Okay, so here's how law applies on reservations:
In criminal matters, it depends on the Indian status of the parties involved. Crimes committed by Indians are never under state jurisdiction. Instead, "major" crimes (murder manslaughter kidnapping maiming incest burglary robbery arson etc) fall under federal and tribal jurisdiction concurrently. In practice, these are almost always punished by the federal government, given their resources and given certain limits on sentencing available in tribal court under the Tribal Law and Order Act. "Non-major crimes" (anything not on the list) are under federal and tribal concurrent jurisdiction if the victim is non-Indian and exclusively within tribal jurisdiction if the victim is also Indian (or pursuant to certain treaty provisions). These you much more often see the tribes prosecute, given limited federal resources to prosecute and the fact that sentences tend to be shorter. (It is unclear whether the federal government can prosecute Indians who commit victimless crimes like, say, marijuana possession; one of the many reasons they are reluctant to try.)
Crimes committed by non-Indians against non-Indians on the reservation, assuming they are not independent federal crimes, are punished under the law of the applicable state by state prosecutors. Crimes committed by non-Indians against Indians, on the other hand, typically fall under federal jurisdiction; certain offenses (domestic/dating violence) can also be prosecuted by tribes. The Supreme Court has also erroneously concluded that states also have jurisdiction over these offenses; this was recent, so not clear how much that will change things. And non-Indians who commit victimless crimes on the reservation can definitely be punished by the state; whether the federal government can exercise jurisdiction here is unclear, though that has not stopped them in the past.
For civil laws, federal and tribal laws apply to Indians. States are presumed to have no authority to regulate Indians on Indian land. For non-Indians coming onto the reservation, whether states can apply their law to these individuals is subject to a complex balancing test that comes from a case called Bracker that looks at factors like off-reservation effects of the on-reservation activity, the compatibility of the state regulatory regime with tribal and federal law, whether value is being produced in or outside of Indian country, the extent of the state activity, and the backdrop of tribal sovereignty.
Whether tribes can apply their civil laws to non-Indians coming onto the reservation, meanwhile, is even more complicated and varies widely by subject matter and by which federal circuit the reservation is located on. There's a multi-stage test you work through, with flowcharts. Usually you think (I think) that tribal law will apply if you are on tribal land within the reservation boundaries, but not if you are on non-Indian-owned fee land within the reservation or just passing through on a right-of-way. You also then look at the relationship between the party being regulated and the tribe (if they have a contract, for example) and whether questions of tribal government or welfare are involved.
It is very sad but it sounds a lot like ceremonial law. That is, the tribes have their jurisdiction until they become a nuisance. If the Federal Government were to be dissolved, these tribes would either sink or swim. Many of them are only a few hundred or a couple of thousands of people. A few of them are a few tens of thousands.
And as S&C said, there could be a situation like a major natural disaster or nuclear war where the global survival rate was high enough that the concept of "society" survived, but low enough where civilization as we currently know it has gone extinct. Think what happened to the Mayans. Their civilization disappeared but its survivor's descendants are still around. At that point, my guess is that a lot of these native people just go back to living how they used to and there really wouldn't be a way to quantify or analyze what they do from an American Legal perspective. I am tempted to think that at least the smaller tribes would either have no survivors or not enough to continue the tribe in any meaningful way but these smaller groups of people, who have already been marginalized, would probably simply lose less since they had less to lose.
The other alternative scenario for the abolition of the Federal Estate that S&C alluded to is that we have a classical Dark Age intermediary period where modern civilization has continuity but our way of life and our current cultural situation deteriorates or changes in a way that is no longer really recognizable as "modern civilization". Basically what happened to Rome in Roman Proper where a series of unfortunate events over the course of a few decades led to a situation where people slowly and then quickly just went off and did their own things. In this sort of situation, I think the long story short would be that everything will happen to the tribes. Some tribes might become completely independent countries, some might experience total continuity with the successor states and societies that host them, and some of them might have their interests rendered totally irrelevant instead of simply only irrelevant when its something important.
