I suspect that once the incursions are in, the event team will turn their attention to elsewhere, and we'll only get a Sansha event if they plan some new thingy for them.
Which is, I think, fair enough. They can only do so many live-events, and there's so much more to the EVE world than just this.
Then again, yea, mixed feelings. FW background story was big when it started; compared FW still feels like a letdown. I fully expect incursions to "fade" in the same way, and while I sort of hope that too (EVE should not be about any one thing), it's also a bit sad.