Lacking federal treaty rights, if people, indigenous or otherwise, wanted to keep other people from encroaching on their land, they would likely use a combination of reason, exchange, pleading, and violent defense.
As to the need for expanded resource extraction (or the potential to move in the opposite direction), a "post-state, post-capitalist future" /could/ create conditions where people wouldn't need to expand access to raw materials, or it could not. If we find it desirable to move towards less production and less resource extraction, we might do so. If we follow the more abhorrent of Kropotkin's ideas and followers, we might drain the swamps for farmland and so forth.
The thing is, there doesn't really need to be a lot of worry about either aspect: people live and have lived for most of human existence without the degree of dependence on extractive industry that we currently do. What we need to look for are ways to do so again (which aren't necessarily the old or traditional ways, but might be). As far as what replaces treaties, whatever it is can't do much worse than the examples of many colonizing nations. Ask indigenous Americans how their treaty rights are working out, you aren't likely to get a positive answer, and especially if it is approached from a longer view to history (though for recent examples google Peabody Coal, or San Francisco Peaks).
