Did you enjoy reading books 1 and 2? If you need an ending, just assume that after the last book the town got rushed by those stone-spider things and Kvothe died with his tale unfinished. Life is messy that way.
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I can't pretend to speak for Rothfuss, but what he's doing while folks wait for Kingkiller 3 looks pretty familiar to my own experience. I'm in the middle of writing and drawing the last volume of a trilogy of graphic novels. I'm constantly fighting to keep it from expanding into four books because I want to finish it around the end of the year; I have a list of things I need to make happen before the ending can make sense. And a list of things I'd love to take time to explore but a strong desire to not make the last volume twice the size of the first two together. And a very ambitious chopped-up timeline structure going on in the last volume.
And yet I've been spending the last month working on pretty much anything else besides this last book; my brain's been excited about a completely new idea for something I want to do about six years down the line (I already have long-brewing plans for my next story), I've been doing art for a convention, working on some short stories I promised. I have to fight myself tooth and nail to get any progress on this nearly finished story. Working on it involves loading a bunch of state into my head, and distilling it down into what is occasionally some very emotionally draining things to write; it is not an easy task. And every page I finish gets me one page closer to the ultra-complicated pages I'll have to draw for the climax, which in itself is pretty stressful - I'll be glad to draw them, but they'll be a ton of work, and I'm not 100% sure the idea I have will actually work, so I kinda want to just go off and do something... smaller. And simpler.
Endings are hard.