I'm sure there's vestiges of them somewhere, but the underlying support (the architecture specific parts of the mach portion of the kernel) is gone for those archs.
I wouldn't be surprised if they keep a minimal Power base maintained behind closed doors. It's how they managed to jump ship to intel so quickly, they never stopped maintaining NeXTSTEPs x86 port
Apple's ARM implementation is in a really good place right now. It would take something extremely compelling to get them to consider any other architecture for an application processor, especially considering that it'd mean giving up some degree of control.
Power is probably not where Apple would choose to go unless something really unusual happened. It's essentially just IBM's pet architecture at this point.
They've been making quite a few changes to the virtual memory code over the past decade, and keeping those vestigial arch's around is a pretty big maintenance burden. It'd probably be less work to just add the arch as if it were new when it's needed at this point since the kernel itself is pretty portable.
