Without Luffy , there would be no strawhats in the first place if the story went as it did.
- Zoro would still be a lone wandering bounty hunter. He would maybe get lost on his way to the grandline due to his own strong ambition, and somehow still make it to the top. He would slap up Helpamo and his father the moment they try to execute him.
- Nami will be an eternal slave to a fishamn while her village gets wiped out. She might consider suicide later on down the line. Arlong will be in for a rude awakening wherever the word gets out, via other stronger pirates or marines.
- Usopp will still be dreaming of becoming a true pirate while playing litte kiddy games, or Kuro would have wiped all of them out, and be living rent free in Kayas mansion.
- Sanji would be a depressed cook who dies without ever having the courage to go after him own dream. Judge won.
- Chopper would have lived his entire life as an outcast in Drum Island, and will have died an outcast. He would die hating his enitre exsistance.
- Robin would have died at Alabasta due to the Croc. No redemption this time around, and no big Ennis Lobby moment. Vivi perishes in this scenario too.
- Franky would have been tortured at the hands of CP9, and the WG gains the blueprints to Pluton one way or another.
- Brook would still be sailing for all enternaity until he decided to commit suicide as the burden of solitude became too large to bear.
- Jinbe and FMI would all still be bottom feeders to the fat bitch called Big Mom.
So, not exactly a happy thought to have.
However, if the question is - who would make the most suitable mc if they're allowed to change plotlines to get the crew under one banner, luffy excluded?
It's going to be Zoro bar none. No question. None.
He possesses the most ambition, and the stongest willpower while actually having a goal worthy of an shonen mc.
Zoro also has a ridiculous disciple and can easily keep others in check, and his starting point is the same as Luffys. At the beginning of East Blue.
Jinbe is a close second, as he's already been shown to be a leader. But how do you go from FMI to the start of East Blue ? And how could you implement a dream worthy of an shonen mc for someone like Jinbe? It's nearly impossible.
Anyone saying Usopp or Sanji needs to lay of the pipe.