I actually wonder about the footprint and hangar space necessary to support a Z-9 vs a Z-20. I think there is a chance that ships which field Z-9s (and Ka-28s incidentally) may be capable of fielding a Z-20 as well.Z-9 will continue on serving on ships with smaller flight decks, those that anything bigger than Z-9 would not fit to operate.
Still, it's hard to imagine that the Super Frelon bloodline can live on this long, when everywhere else outside China it has long been replaced.
As for Super Frelon longevity, that is true to an extent but it isn't alone. Ch-53K is the latest variant of the Ch-53 family whose original first flew in the early 1960s as well, not to mention Chinooks.