From episode 173, Chibiusa died. Since his father dies, so by default the future has changed.
The concern comes from Sailor Pluto, being the guardian, she should have noticed this and yet nothing was said.
Once the galaxy is saved, everyone comes back to life, so by default, Chibiusa too. But since she comes from the future, it's normal that we don't see it.
The timeline takes the right path to go into the future that we know.