Well first of all the indigenous nations as cultural and political entities still exist and still claim territory stolen by the settlers. The majority of settler owned land will be taken back into indigenous sovereignty. Many nations including the Americans and Black people will want to use the same resources. They can share through agreements reached in decolonial states. In my prediction, these states will be confederations between the peoples that inhabit and use the lands and resources in question. Equality of nations rather than equality of individuals will necessarily be the lower stage of Decolonization where individual equality will be gained towards the higher stages as the decolonial states wither away. Africans in the Americas are nations born into world through their struggle against slavery and colonization, but we must be careful reactionary ideas such as a Black Belt state as there are indigenous nations who claim and live in that region still.
Any system where Americans exercise political supremacy over colonized groups will necessarily reproduce settler Colonial relations. There will be no reforming the American annexationist system, only the the de-fanging of their previous annexations and thus their access to further annexations and Imperialism.
I am very much in favor of decolonization but this is pure idealism and a recipe for disastrous defeat. If this is really the political platform that indigenous revolutionaries intend to adopt then there is a major risk that the settler colonists will simply decide it is safer to complete the genocide of indigenous people to the last person, as such a plan will be perceived as an existential threat. There is very little chance that the settler majority will allow itself to be turned into second class citizens in what they view as their own land. The fact that it is in fact stolen land may give indigenous people the moral high ground but it does not change the reality of which group has the numbers and the power to dominate it.
A minority cannot rule over a majority for any extended period of time and even to attempt it requires massive violence of the likes we saw in apartheid South Africa and which we are seeing today in the Zionist entity. It is why the Zionists are attempting to demographically engineer a settler majority in the stolen land. And it is a fact that indigenous people in the US are a very small minority, in fact without the allyship of other colonized nations trapped inside the US prisonhouse of nations, such as the black and latino populations, they stand almost no chance of taking even the smallest chunk of land away from the settler state due to their numbers being so small. They will simply be brutally crushed.
Any viable strategies will have to involve allyship with a portion of the settler proletariat, possibly to arrive at a model similar to that of the USSR and the Russian Federation, with national republics on specific territories where the minority nations hold a majority. This will involve population transfers, there is no other way around it if you don't want minority nations to be politically dominated by the settler majority inside these new political entities, a state of affairs which you rightly point out carries the risk of a reproduction of colonial dominance relations.
Whether or not the US as it exists today will be dissolved and experience secessions by then does not change this logic, because there is no contiguous territory in the continental US that both lacks a settler majority and is capable of supporting an independent state. In whatever states secede from the US settlers will still be a majority and the revolutionary strategy will still require involving at least a portion of them, which is only possible if enough of them perceive the revolutionary project as being also in their interest. You don't win people over by promising them that they will be politically disempowered if you win.
Instead of fantasizing about the impossible turning back of the historical clock to pre-colonial times, which, while it may feel morally righteous is not realistic as it does not take into account the material realities of the world as it exists today, i would instead start thinking more practically about how the inevitable war against the settler state will be organized. What will the political leadership structures of the revolution look like, where will the manpower, the material and the logistical support come from, how will the population that supports the revolution be fed, how will the blockades and the bombings be withstood?
You literally do not understand that the American nation "owns" 98% of the land but occupies around a quarter of it. This land is owned only for the purpose of extraction which allows Americans to live far beyond their means. This territory, the majority of territory in the US and Canada, will be taken from them. If you'd study the land question in the US you'd understand what we're talking about. This is a matter of state and sovereignty, the Americans aren't entitled to their own sovereign state, only a decolonial one. There is no point in time to return to. The conservative, reactionary position is settler sovereignty over the lands.
There is no idealism or moralism except the white guilt and entitlement, to land they don't even use, felt by settlers. The Americans are already genocidal, and we know that they will seek a final solution to their Indian and Black problem. There are tens of millions of us colonized, and there will be tens of millions of white comrades to fight with us.
Every revolution is a fight for survival. Ours has been constant.
California has over 10x the population of Nevada. Should California be entitled to 10x the land of Nevadans? No, it's nonsense. The population of a people is dependent on the resources which they have access to. Americans are not entitled to their annexations, most of which is reserved for future exploitation while they suck the rest of the world dry.
This is where international solidarity is required. The number of people colonized by Europeans is far far larger than the Europeans occupying the Americas. The indigenous nations of the Americas don't need to worry about being a minority when the majority of the world recognizes their sovereignty and understands that the super structural basis for that sovereignty is critical to their own. The settlers in the Americas will be dispossessed by a coalition of the global majority, not by the slowly recovering indigenous populations of Turtle Island.