Okay, there's a picture of the cast and crew celebrating the recording of the final episode with a cake, so that's another bit of proof that it's ending. And also, that sounds to me like they ended it on purpose! It's over, and I can guarantee you a petition won't help.
...they knew that they recorded their final episodes. So if your petition were to work, we would have a ninth season, despite the eight already ending it. I'm not sure how it's going to work, asuming that petition will change anything. If you hadn't already, put it on the Regular Show's wiki.
I don't know what else to tell RS fans. If you guys can't accept that the show is going to end, after all these tweets pretty much confirming it, I am at a loss of words for you. I'm not criticising you, I'm sure when AT is ending, I won't believe it either.