The replacement will be destroyed. This arc is set to disrupt the entire balance of the world:
1. The World Government losing an Admiral
2. 3 Yonko all being 1-2 poneglyphs away from the One Piece
3. A Gorosei in danger
The world is set up to go completely of kilter. And the destruction of the seraphim and the balance of powers just goes along with that. As I said, story wise, the abolishment of the Warlord system was in order to trigger the creation of cross guild. That’s going to be the big effect on the world. The seraphim were just a plot device to give an in verse reason for why the WG would approve of the warlord abolishment. They can easily get destroyed and it not effect the story.
The balance of the world was already upset with the end of Wano & dissolving the Shichibukai.
The point was also to show the WG getting stronger despite that, not getting even weaker before the Pirate King even comes knocking at their door.
You don’t diminish your final antagonists before they even take the stage.
Again, that’s like proposing that Blackbeard will lose to Law or Garp before even facing the Strawhat pirates. It’s kinda ludicrous.
Not sure why you seem to hold Cross Guild in such high regard.
Again, they’re still the weakest link among the Yonko…and having 1 joke Yonko crew with the least relevance that’s only going to be even more irrelevant when Luffy is crowned Pirate King wasn’t the resolution to a plotline to make the WG even more dangerous by shedding them of the unreliable Warlords.
The WG is still the ultimate antagonist of the story. Cross Guild is just an amusing side note along the way.