I think it's weird all of this.
I think something might have happened during the rehearsals in Australia. Maybe Steve didn't want the issues of the first leg and he checked Nicko's playing and checked if he resolved his issues playing. and get a talk with him and the rest of the band and management and raise the Nicko's retire on the last gig of the tour. And he took the decision of bring his alt. band touring with them and check his drummer and tell him. Learn all the songs of the tour if something happens.
I think there are pictures taken by Rebecca in Sidney where Nicko is looking at horizon, smiling but with sadness in his eyes like that would be the last time to play there. It's like, ok. I'm going to spend some days alone with my wife reflecting and assimilating all this.
If this is the truth and Knowing all of this, I think the management fooled the fans launching the 2025 tour selling tickets knowing that Nicko wouldn't be there.
If Nicko took the decision the last week, well, it's absurd because he has been playing much better than the first leg and the first gigs of this leg. By the other hand If this were true. Steve, the management and the band could have taken his time and thinking about who could replace Nicko.