McGregor briefly reprised Obi-Wan for a voice cameo in Star Wars: The Force Awakens, which also included archived audio from his predecessor, the late Alec Guiness.
It was also rumored late last year that the reason the Obi-Wan movie hadn’t moved sooner was because there are plans to use him in the remaining saga movies, i.e.
The Last Jedi and/or Episode IX.
While it’s hard to imagine anyone else but McGregor playing Obi-Wan for this spinoff given that he’s the right age to play the character in this period of Star Wars history, we can’t rule out that Disney and Lucasfilm may decide to hire a new actor to don the Jedi robes.