Say what you will of SM, there's no denying the fact that it finally broke the stagnancy surrounding the anime for a long time, breaking the same old story pattern and setting Ash of on a new path. Say what you will of the Alola league, but it is an official Pokémon league ash finally won, setting him on a new path
The writers clearly show Ash taking the next step towards his goal of a Pokémon master. He is actually portrayed as a veteran strong trainer in the start of the series, instead of Ash and Pikachu losing against an elekid, snivy or a surskit or struggling against mimikyu, this series right off the bat has them completely trounce a Tyranitar and Gyarados, showing them as strong off the bat and being a mentor to the rookie Goh, him easily winning his way through a tournament and his first capture being a freaking dragonite. Then they set up his endgame goal of beating Leon, who's not only a champion, but a world champion, the strongest trainer in the world by the narrative (rip Cynthia fans). This series has clearly set up for ash to take on Leon and defeat him by the end of the series, becoming the world's strongest trainer. However unlike what others imply, this isn't the end of his journey simply coz they brought up in this series being a Pokémon master isn't just being best at battling and that beating Leon would be another step for his goal. So clearly Ash continues for atleast one more series. However as SM shows, Ash winning the PWC would more heavily change his story path and dynamic as the series goes on. He would be the world's strongest trainer, even if he isn't shown defeating Cynthia and all, by the narrative, becoming the world champion and beating Leon helps him become the strongest trainer. Clearly a huge shift in story would be required to carry Ash forward as they have gone away with just rebooting him. Personally I would like to see his next journey revolve around him pondering on what a Pokémon master is for him, being bored after being the world's strongest, and I hope the next series would be his last. But more likely he just gets another plot in the Gen 9 games that is battle focused to do, although what could top the PWC in terms of lore
Chloe is definitely leaving after the series ends, I can see her becoming a research partner and helping her dad with his book in the end.
For Goh, I'm mixed. On one hand people do think he would leave, he has a gen 8 Mon as his starter, he has an engdame goal potentially set up with Sonia in darkest day. But on the other hand, Goh seems like such a pivotal character on his own. His name, Goh, representing such an important part of the franchise now, his goal being large enough to continue on if they wanted. Cinderace always had an arc of wanting to protect lesser mons, maybe in the end of Journeys Goh releases Cinderace to do that and so in the next series his mascot can be a Gen 9 Mon. I can easily see both options happening, although I am more on the train of Goh leaving considering the Sonia goal, I personally hope we don't have that much Pokémon Go representation in the anime moving forward, although I do like the idea of the anime now promoting the franchise as a whole instead of just the new games.
Whatever is in the future, it definitely isn't predictable as it once was and would really shake things up!