When I consider the interplay between nonviolent civil resistance and a negotiated end to a most foul regime, I think about several luminaries and their wisdom.
First, Dr. King, who wrote in his canonical Letter from Birmingham jail:
"You may well ask, "Why direct action, why sit-ins, marches, and so forth? Isn't negotiation a better path?" You are exactly right in your call for negotiation. Indeed, this is the purpose of direct action. Nonviolent direct action seeks to create such a crisis and establish such creative tension that a community that has consistently refused to negotiate is forced to confront the issue. It seeks so to dramatize the issue that it can no longer be ignored. I just referred to the creation of tension as a part of the work of the nonviolent resister. This may sound rather shocking. But I must confess that I am not afraid of the word "tension." I have earnestly worked and preached against violent tension, but there is a type of constructive nonviolent tension that is necessary for growth."
Then, I turn to Bill Ury and the authors of Getting to Yes, who first taught me about the BATNA, the best alternative to a negotiated agreement. It's something a party to a conflict should be quite transparent about. For example, "Okay, ruler, we need you to either honor all human rights and civil rights or step down, and if you cannot manage to do one of those two things within the next four weeks, we are going to begin a deep national nonviolent resistance campaign that will impose some serious costs. This is your choice." In other words, Ury and Fisher might have called what Dr. King wrote about as a perfect example of the use of a BATNA. Dr. King and the movement didn't stop nonviolent civil resistance until they were invited to the White House to negotiate, which ultimately resulted first in the 1964 Civil Rights Act and then the 1965 Voting Rights Act.
The third scholar activist who comes to mind in this is Mary Frances Berry, especially her 2018 book, History Teaches Us to Resist, in which she cogently explains all this as the inside game/outside game. The synthesis of them can look exactly like the above Civil Rights Movement example or any number of other uses of nonviolent civil resistance (the outside game) to drive actual policy or even regime change (inside game).
Nonviolent resistance is not necessarily working outside the system, in other words. It is a legitimate tool for the goals that have temporarily exhausted all the available legal inside game avenues.