I now nothing of what is happening with the pipe line however I'm sure there are legal precedents in place that might dictate what might happen due to the action of the tribal leaders. They may have to wait and see to ind out if litigation is effected. Since I don't follow this issue personally, I can't give a full opinion about it.
Yes, whatever deal the tribal leaders made or whatever action they took prior to their suit most likely sealed the ultimate fate of the litigation. There is precedent for the Standing Rock suit. Attorneys will be sure to check and bring up whatever happened before the suit in order to make and win their case.
As fas as this researcher has seen, there was no action by the tribal leaders that should affected the outcome of the litigation process. This appears to be yet another example of huge corporations overpowering ordinary citizens. The fact that there is an ongoing attempt to fun these tribes off from their land is appalling. From available research this tribe was protesting peacefully and the attacks on them were not justified.
It was the corporations and the fact the local law enforcement and the Governor of South Dekota has an invested interest in the corporation that wants to build the pipeline that "sealed their fate". These kinds of conflicts of intrests are becoming an increasingly difficult problem in the new administration.