I don't see any purpose in them splitting up again.
We don't know the full context of what went down with Arabasta yet, or with Sabo. Remember how Oden landed at Wano with the Roger Pirates and knew something was off? How he knew that he had this one opportunity to conquer the world with Roger and live out his true dream? That will be Luffy post-Wano. He will have 3/4 Poneglyphs (likely), and the crew will very likely be a huge target to literally everyone as information about how to read the Poneglyphs and find Laugh's Tale become more wide-spread (Hell, Law knows). People will be after Robin. They will be attempting to take the Straw Hat's possessions (Poneglyph rubbings). They're stronger together and need to protect what they have. I honestly think after Wano it's going to be a rush to become the Pirate King as finding One Piece feels more like the first domino falling in the end of the Tenryuubito system.
I think the more realistic expectation is the next time a huge confrontation with the WG happens (Final War) will be after Luffy has already become PK. He'll have the Grand Fleet + Bellamy, potentially some Supernova who are less interested in being PK, possibly the Revolutionary Army, and potentially some old "enemies" who hate the current system (I imagine Smoker, Fujitora, Aokiji are going to struggle to fight on the side of the Tenryuubito. Anyone who doesn't believe in absolute justice will falter).
What I expect:
- Confrontation with Marines after Kaido
- Stop by Elbaf in the New World. Dove-tail into the giants joining Luffy's alliance for the final war with Loki behind them. Potentially could be a "final confrontation" with Big Mom here.
- Blackbeard Pirates try to or succeed in stealing Robin and Poneglyphs
- Blackbeard may (probably) have the final Pongelyph.
- Blackbeard will have a huge fleet and be extremely dangerous. This could potentially be a large-scale war like Wano as he has many fleets under him now.
- Robin refuses to read the pongelyphs to him resulting in him not becoming PK.
- Luffy and the Grand Fleet invade Hachinosu
- Blackbeard defeated = all four poneglyphs + Robin to translate.
- Luffy core group (Zoro, Nami, Usopp, Sanji, Chopper, Robin, Franky, Brook, Jinbei, Yamato at the least) land at Laugh's Tale and read the Rio Poneglyph
- Unlike Roger who was dying, and the timing not being right (Poseidon hadn't been born yet. Nor had Momo), Luffy will have the tools to take on the WG. He will beckon the Fishmen to the surface in Noah with Seakings leading them / Shirahoshi.
- Marineford will be a showdown.
- Luffy side = Dressrosa, Wano (Momo possibly being Uranus), remnants of the Beast Pirates, the Grand Fleet, possibly Crocodile's crew, Straw Hat Pirates, possibly the Heart Pirates, some rogue Marines who don't believe in Im ruling the universe, Elbaf, Poseidon (and Sea Kings), Zou / the Minks, possibly Katakuri and a subset of the BMP who respect him, Revolutionary Army.
- Marines side = CP0, Admirals / Marines, new weapons by Vegapunk.