What if Dipper had thought a bit more before accepting the offer? Spoilers for "Dipper and Mabel vs. the Future." All characters belong to Alex Hirsch, not me.
Not Getting Stupid
"Listen to me, Dipper: this town is a magnet for things that are special. And that includes you and me. It brought both of us here for a purpose. Stay here with me, Dipper. Become my apprentice. Don't let anyone hold you..." Ford said, interrupting himself to cough.
Dipper was about to say he would, when a thought ran through his mind, "Promise me you won't get stupid." Where had that come from? The night they heard the story of the two Stans, Mabel asked him to make that promise.
Dipper could see the parallel; the split between the older Pine twins started when one was offered a great opportunity and the other was going to be left behind. But this time, there might be another way.
"I'd like to, very much. And... could Mabel stay, too?"
He offered Great-Uncle Ford a hand up out of the trench the prison drone had dug when it fell from the sky.
Ford took Dipper's hand and pulled himself up. He wasn't smiling. "The offer is just for you, not Mabel. I like her a lot, but she's a bit too silly for this kind of work. I can't take you both on as apprentices. Didn't you hear my advice not to let anyone hold you back?"
"Mabel is smart in her own way," said Dipper. "She doesn't hold me back. You're thinking of yourself and Grunkle Stan; it's not like that with us. Her thinking outside the box has saved us more than once. She was the one who found out that gnomes are vulnerable to leaf blowers. She solved Quentin Trembley's map by thinking like he did. And don't forget how she got us the unicorn hair."
"She just used brute force against those annoying creatures," said Ford. "I won't tutor anyone who isn't up to a high standard of intellectual accomplishment, like you."
"You wouldn't have to teach Mabel. She could go to regular school here, and work with Grunkle Stan when you and I are busy."
"Stanley won't be here," said Ford.
"What do you mean?" asked Dipper.
"I mean I've asked him to leave this house at the end of the summer. I'll take my house back, my name back, and close the tourist trap business for good."
"What? I can't believe this! You're kicking Stan out? Where will he go?" asked Dipper.
"I don't know and I don't particularly care," said Ford. "It's my house and I want it back."
"It wouldn't be your house now if he didn't spend the last thirty years making money as best he could and paying your mortgage. Someone else might have found the portal, and who knows what they would have done with it?"
"It could hardly be any worse than what he did. Re-opening the portal was an insane risk. Now we have the rift to deal with. He shouldn't have done it."
"You asked him to."
"No, I didn't."
"The last thing you said as you were being pulled in was, 'Do something!'"
"I meant something quick, like shut it down before I was pulled in."
"How could he know you meant that? And even if he did know, I'm sure he would have gone ahead anyway. He cares about you."
"He's stubborn, that's for sure. He'll find a way to survive without his Mystery Shack."
"Please, can't you let him stay and keep his livelihood?"
The present situation is just unworkable for me. With all his criminal shenanigans, my good name has been dragged through the mud."
"People love him anyway. He's funny, and charming. The name of Stanford Pines is pretty good in this town."
"I don't see why."
"You've been away in dark dimensions too long. You could learn something from being around Grunkle Stan and Mabel."
"I'd rather work just with you."
"What about Soos, and Wendy? Where will they work?"
"I can maintain the place myself better than any hairless gopher handyman. And with no gift shop I won't need a cashier. I just need you as my apprentice."
"I'm having second thoughts about that."
"Don't you see what a wonderful opportunity this is? You can be my partner in research and inventions, just like Fiddleford McGucket."
"Just like McGucket? You know where he ended up? He's living in the dump as a half-crazed hermit, the town kook."
"Poor Fiddleford. I didn't know that."
"You never asked. Once he stopped working with you, you pretty much forgot about him, didn't you?"
"I couldn't trust him once I knew his mind might have been tainted by Bill."
"Maybe. I think you could have helped an old friend a bit more."
"I guess you've definitely decided against taking my offer."
"Unless Mabel and Grunkle Stan can stay as part of the deal. We need them to balance us. I do, anyway."
"I'll think about it. Right now, we have to go home and seal the rift."
"Mabel, I just had a wonderful day. UFOs are real and there's one under the town and I saved Great Uncle Ford's life, and..."
Mabel jumped up from the bed and gave him a big hug. "I heard everything you said on the walkie-talkie. Thank you for standing up for me, bro-bro! I had a terrible day and I don't know what I would have done if you had said you were leaving."
"You heard it all? Then you know we have something bigger to do than planning our birthday party."
"Yeah, forget the party. All that matters is that in one week Grunkle Stan is going to be homeless. We have to find a way to help him."
Bill, as Billendin, waited in the woods as it started to get dark. He spoke to Blendin, who hovered as an invisible spirit nearby.
"This isn't working. I really thought I was going to trick Mabel out of the rift. Well, I still have a time machine. I'll just go back to the day the portal was reopened, and get access to the rift before it can be contained. Less fun, but it should work out just fine!"
Lolph and Dundgren appeared beside him. Lolph grabbed away his time machine tape-measure.
"Blendin Blandin, back meddling with the time stream again!" said Dundgren. "It's back to the Infinitentary for you!"
"That would be too boring for me," said Bill. "Here, you take this body back."
"B-but my deal was to visit the time of Dipper and Mabel again without getting in trouble with the Time Baby," Blendin protested in spirit form.
"You wouldn't have, if it had worked out for me to take over the world," said Bill. "As it is, just try explaining that you were possessed."
"T-take over the world? Is that what you wanted?" asked Blendin.
"I'll find another way, even if it takes another generation or two," said Bill. "But for now... the universe is a hologram, buy gold, bye!"
Ford came up the stairs to the bedroom and called to Dipper. "I need to get the... the object we were working on."
Dipper produced the rift container from his backpack. "You mean this?"
"What is that?" asked Mabel.
"A dimensional rift, something left over when the portal broke. We have to seal it so it doesn't break and let Bill into our dimension," said Dipper.
"You were supposed to keep that a secret," said Ford, frowning.
"I know, but I'm through hiding things from Mabel," said Dipper.
"You're a big meanie, Great-Uncle Ford," said Mabel, with tears in her eyes. "Not only are you kicking out me and Grunkle Stan, you kept us in the dark about important stuff. I think I'm starting to hate you."
"I... I don't know what to do anymore," said Ford. "Dipper's right, I may have lost some of my humanity in my devotion to pure science, and everything I had to do to survive in the other worlds. I think I should try more of your way."
"You mean..." Mabel said.
"If we can get the permission of your parents, both of you can stay in Gravity Falls. And Stanley can keep the Mystery Shack going."
"Woop woop!" said Mabel. "I love you, Great-Uncle Ford!"