Don't worry, I'm terrible about forgetting to review too. And I'm an author! You'd think I'd remember every time. Not so! lol! So I never worry about whether someone does or doesn't — they could be just like me and flake out a bit at the end.
And yes, I wonder too about how many people were discourage, disappointed or just feeling burnt in general by the ending and that's turned them off from the fandom. And the rabid wave of NH/SS shippers after the ending didn't help either. I'm sure that played just as big a part in turning away fans.
It took me a while to get back to being comfortable with my fanfics again. Honestly, I was really afraid I might feel so burnt I might just drop it. Plenty of writers and artists already have. But there was solace in the fact that it wasn't just NS that was overturned. It was every theme, every character, everything I originally liked about the story that was thrown out the window. That took the sting out. It wasn't just a snub to NS, it was the unraveling of the whole story.
So after the initial shock wore off, then I realized that I had to finish my stories just to give myself some closure. I have never been super crazy about the manga or anime, yet I always hoped the themes that were there would be explored. But they weren't. (I started reading just before the Pain arc, and after it ended was excited to see what was going to come next. If only I'd known!) So the fanfics have been the best thing I've gotten out of the series, which has helped me improve my writing, while fixing things in the plot I wished they'd show. And I couldn't let the go unfinished.
Kishimoto might have botched the ending of his work, but that didn't mean that I had to botch mine!