Thought I had heard that it was supposed to run for 3 seasons. But, this definitely looks like a show that is wrapping up. Still, better that it ends at 40 total episode which each one of those episodes being incredible than dragging on long after the show had exhausted its premise.
I think Disney has been trying to stretch the show out, which is why sometimes episodes hardly air. It's annoying, but I'm guessing that's the reason. Anyways, I wouldn't worry about the show being cancelled, especially this far in.
I actually read this last episode very differently. Yes, they are wrapping up this story line and approaching the end of summer. This was inevitable, It would of felt really weird to have summer last any longer than season 2. But the developers have always maintained that the show will end with summer ending and M&D going home. Ep 17 gives us an alternative to them going home. Unfortunately, the show makes it clear that this apprenticeship is going to play out as a parallelism to Stan and Fords relationship. So Dipper will at one point have to show Ford that, no a twin sibling is more important that science. But still, they have opened up mechanically how one or both twins could end up staying in Gravity Falls.
Alternatively, the weird-ocalypse has begun. Which could twist space and time in unexpected ways. Creating other ways for them to stay, or for the weirdness that is GF to follow them home.
Or maybe Dipper and Mabel could return to Gravity Falls next summer (2013), if the world doesn't end, and Dipper could be Ford's apprentice while still spending a lot of time with Mabel.
Since Mabel didn't think about her presumably still living parents at all when bemoaning her pending separation from everyone she cared about, perhaps something could be worked out where Dipper and Mabel permanently moved to Gravity Falls, living with that odd couple Stan and Ford, and attending the Gravity Falls schools and Dipper at least getting tutored by Ford.
As a somewhat newcomer to the series, only having seen season 1 so far; here I was hoping to find written confirmation, that the series would go on, for a thrid season in the new year?
Unless someone else has confirmation of it ending, I'd wait before saying it is over. Disney picked up GF for season 2 months before they announced it (which also likely means Hirsch and crew know their fate already) and Disney announced it days prior to Gideon Rises. In other words, we may not know for several weeks. And I highly doubt that Bill's messing with this dimension won't have some sort of consequences, which might need to be explored.