I’ve heard some strange stuff from the newspaper headline of “Stan Pines Dead” but trust me, I have a logical answer, and probably much simpler than what others are thinking. Main speculation is that either Grunkle Stan is pretending to be his brother, or somehow they switched bodies. I do understand body-swapping because of the electric carpet from “Carpet Diem” that was in what many are saying Stan’s brother’s room, but I have a much simpler idea on the matter.
I’ve heard everyone call Stanford’s brother “Stanley”, which really sounds like something Gravity Falls would do. In that case, STAN Pines being “dead” could just mean that they meant Stanley. He probably held some kind of importance to the town at the time, considering McGuckin worked with him, and everyone was curious how he disappeared. Considering how at the time people were erasing the townsfolk’s minds from the supernatural, they just simply covered it up with a car crash story to stop speculation. In this case, Stan was somewhat doing the right thing in his own mind, even if he could run a few risks, he just wanted his brother back.