Zoro would have kept to strive to become the best even if alone... yet or he died episode 2-3 aka Axe hand Morgan kills him or maybe the fact to strive for other people (like Mihawk says) helped him to become stronger than he was alone. Anyway it seems Mihawk manged to achieve the WSS lone wolf style so..
Nami had the problem that she was tied to Arlong and her village and that was difficult to shake off without a powerfull good samaritan type of guy. In any case Nami would have had to join a crew in order to be able to achieve her dream, she can read the weather but she needs protection, a ship willing to go wherever she wants to make her charts etc. so a whole crew willing to listen to ther and her dreams (byw when was the last time we saw Nami talk or work on her dream?).
Sanji would have stayed pretty much on the Baratie if another special crew didn't show up (and that had to be a special crew along with a special situation like Krieg), maybe in time he would have set sail alone to find the all blue but we don't know that. Most likely as soon as he found a woman willing to listen to him he would have set roots there and ended his voyage.
Usopp would have stayed in his village to be slaughtered by Kuro and friends, and if not I'm pretty sure his voyage would have been pretty short and with a tragic end. Usopp is somewhat of an hero but still a normal guy (who likes to talk big, and if you have not Luffy or Chopper in front of you but piratemoron#123 you are in trouble).
Chopper, he most likely would have stayed on his island along with Kureka if not for a special situation (see Sanji), yet let's say he wants to broad his knowledge and achieve his dream so much that he leaves his island he would have faced a massive wall called racism (be it by discrimination or wanting to sell him as a rare beast), a talking deer who can transform is for sure weird stuff. He alone, considering also how naive he is, would have neded up in Sabaody auction or directly in some noble zoo or something like this (even end with BM, who knows). Maybe he could avoid (but how much?) this racism wall by showing his amazing skills as a doctor which for sure are needed left and right but he should have at least the chance to show them which is not assured, not at all. Also unlike Usopp he can defend himself but up to a certain point (also again his naivety doesn't help).
Robin is smart, has survived on her own for decades even as a child and Aokiji stated that she would have been able to escape alone even from CP9 if she wanted to. Yet escape is different from achieving her dream. She maybe should hit her wall when she had to read the road poneglhyps aka steal them form yonkos. She could ally with them but just one and at that point she will be a bird in a golden cage, she will be even mroe precious than the road penglyphs for a yonko (ask BM) so live a good life but not be able to leave Wano/WCI. Maybe BB would give her mosre freedom, Shanks or the Revos could be the best alternatives yet (they think alike and also have the power Robin needs to go search for Poneglyphs and maybe are willing to lend her this power).
Franky, he had his family in Water7, let's suppose a special case again and he set sail: he would have to find a crew and since he can bring in his dream ship and skills that are looked for as well (naval carpenter) he would for sure find a good (for sure there are plenty of crews who can accept him even if he is a bit weird, we have seen plenty in pretty much every crew). Anyway Franky's dream is pretty much achieved the moment he has done the ship, then it is the ship that has to demonstarte it can navigate in every kind of sea. Aka make another one which was on par with the Orojackon (which was also the only other ship made from Adam wood aside from the Sunny). Tom did the same and didn't have the need to sail along with Roger (was it so?).
Brook. He would still be stuck in the Florian triangle like the decades before, really a sad destiny. That at least until somebody defeats Moria. So if Moria feel confient enough to go challenge Kaido wait for that moment so that maybe distance can make his pwoer disappear or simpyl wait for Kaido to smash him like Luffy did.. anyway another bunch of years if he is lucky.
