The only friends I can see returning are Iris since she is Unova’s Champion, Bonnie and Max if they aged enough to go out on their own journeys (preferably together as I think that they have potential to be good friends), all of the Alolan friends including Gladion and Lillie, Goh, Dawn, and Serena. Misty and Brock have too much history with Ash that them returning without him feels wrong, May’s Japanese voice actress retired and I feel like she has accomplished enough to not need to return, Cilan because he was honestly boring as a character and had mostly a one note joke that got old REALLY fast and that’s why I think he shouldn’t return and Clemont shouldn’t because Bonnie should be able to have her own adventures without her brother around all the time.