No matter how good Neymar is, would have been able to stop 6 goals? Some may argue after the first two it Brazil gave up and Germany's momentum led them to score the other 5. However, I don't think he could have made that big of a difference. Perhaps the game might have ended 3-1 or 4-2, but Germany was going to win that game no matter who showed up for Brazil.
I do not believe a healthy, striking Neymar would have made a difference in the World Cup semi-finals. I believe it comes down to skill and being focused. The reason why Brazil lost to Germany in the World Cup semi-finals is because the skill levels were different. No matter how many times Brazil may have won in the past, it makes no difference for present and future games. Brazils skill levels were just too different compared to past games and simply couldn't keep up with Germany.
I don't think it made a diffrence whether Neymar played or not. They might have still loss the game. No matter if your star player isn't in the game the rest of the team should still play their hardest; and they did. It just didn't pan out the way they hoped. Everyone just had high hopes for the game. You have to admit Germany has a pretty decent team.
With Brazil's humiliating defeat to Germany, some want to shift blame to the missing players of Brazil's squad. The fact of the matter is, Brazil's defense was in shambles. Bringing on a very talented striker would not solve this problem. No one single player could overturn the result that came into effect in that game, it was a team wide failure.