The collapse of the Brazilian national football team does not depend on Neymar being in charge of the squad, but in my observation there are many factors that cause the Brazilian national team to become as usual. Brazil, which was supposed to be the strongest team in the world cup, is now just a memory, since 10 years ago, twice in the world cup competition, Brazil is no longer a squad that is feared by opponents.
The reason why all this happened, Brazil does not have a successor like Roberto Carlos, Ronaldinho and also several other senior players, so I don't think the Brazilian national team will return with the best performance if just rely on Neymar.
This problem has indeed been faced by Brazil for the past few years. In addition to not having a senior player who can be a role model anymore, like Neymar in the past, many young Brazilian talents have been brought in by big European teams to be educated, and have made them not have the traditional Brazilian football playing style because they have been abroad for a long time. They do not have enough playing time in the country and cause the younger generation not to have good skills to inherit from the older generation. This causes the structure of Brazilian football to gradually erode and decline in quality. If they want to return to their glory days, they need to evaluate their transfer system in a big way, limit more young talents abroad and prioritize creativity, flair, and tactical instincts characteristic of Brazilian football to their younger generation.
Brazil developed the stars for Europe, but now their clubs are rich enough to bring them back! Memphis Depay, Jamal Lewis, Felipe Anderson. Now, European teams are dumping players in Brazil! Though it starts with young development rather than only imports, the power is shifting.
Clubs won't have to sell teenagers to survive if their financial growth maintains. Imagine if Endrick, Estevão, or Vitor Roque stayed in Brazil until 23, as Viníça Jr. should have? The league would exploded! The model is keep stars, draw European dropouts, rule Copa Libertadores, then take back the globe. The "Brazil as a feeder league" era needs to die.