I understand but the assumption here is that the treaties would no longer be in effect since the Lakota’s would have withdrawn.
I see your assumption. However the very existence of the assumption implies that the secession is legitimate, which blows the rest of your argument out of the water. Either the People of the Indian Nations deserve to have the treaties signed, fulfilled by the United states, which not all of them are, or they don’t. If they don’t then by definition you are classifying them as either unworthy of having them fulfilled or to the rank of second class citizens, the very point that this movement is trying to make. Both of which I find unacceptable. If not a direct contradiction to the letter and spirit of our own Deceleration of Independence.