Almighty Zard
He has returned.
Ash might very well still stay, but even I refuse to believe the staff would be so tone deaf to the point that Ash just casually continues in Paldea as though nothing happened. You just don't do a power of friendship victory with all the recurring characters just to ignore it.
If it's still Ash, maybe a timeskip, or a reboot of the whole anime could happen, basically something significant.
Agreed, the intensity and prestige levels are too high to make resetting Ash as he currently is plausible.
They would pretty much have to reboot the show entirely, to do that again.