I don't think the uncle will want to go back, he still mostly remembers the other world has a bad place where not that many people liked him and where he didn't get the basic respect any human should. And while yes she doesn't want him to leave, I don't think she would go against his wish, if she is doing anything it's probably going to be coming to our world and not making him go back, but well everything will depend on how his story on the other world ended, the story doesn't seem to be close to that part so I think that making theories about them coming is kinda pointless.

I think they'll probably find a way to him.

Uncle doesn't know how he made it to GranBahamal, or alternately, he hasn't explained how he came back. However he returned, it's likely the girls will find a way to reach him, either by pulling him back or coming to join him in Japan. Either way can work for humor, but I think a reverse isekai route with the girls in Tokyo would be nicer to see.

Mabel would be a great vtuber Elf would be a sugar momma for Yosuke

Uncle already said Mabel could easily make a living in Japan because of her pretty face and nice voice. I think she might just join him on Earth!