My question to you is can Neymar single-handedly lead the team to victory. No it is not possible because all the players of that team have to perform well to win then that team can reach the desired win target. Moreover, Neymar Jr. has been out of football for over a year now, and there is no guarantee that he will actually return to his true form, i.e. old form. So even if he returns to the team in this condition, it may take time to improve his performance.
Currently Brazil team is performing very well, in the last two matches of Brazil we never felt that the absence of Neymar in the Brazil team made them a weak team. However, it is true that without Neymar Jr., Brazil's attacking side is weak because he is still one of the best forwards in Brazil's current time. Adding him to the team will increase their team's strength but it does not mean that his team will be able to win if he is added to the team.
I do not think Neymar could do that, there is no way Neymar could be considered that good anymore. He used to be that good, he could have done this back in the day, but not anymore and he is not that much of a help when he plays neither so him not playing isn't even that bad for them.
They should be able to get wins without him, they have a squad of players which are good and I believe they are going to end up with a great profit when it comes to betting on Brazil as well because I believe we are going to see them play better now. They did had a horrible period but they are good players and they should not have a full time going like this, there should be a moment where they are no longer that bad and they are doing better.
I believe we are going to see them have this kind of approach and we are going to see them have some trouble recovering from the situation as well. The looks of the current situation seems like we are going to have some trouble if they keep on getting worse.
So the only possible way for them is winning, because if they lose, they won't be even in world cup, and they are losing reputation as well. They will win just to recover and participate in world cup, and betting on them to win is smart.