I don't actually understand this.
Is Nintendo important to the home console industry? Of course, they're one of the primary hardware and software companies in gaming. Are they more important than the others? Probably not. If they exited tomorrow, developers would rush to fill that niche, including former Nintendo employees. Platforming fans would either have to migrate or quit gaming.
Now, as far as handheld gaming goes, they are more important, though that importance has been mitigated by mobile phone gaming. In Japan, Capcom would release a Monster Hunter for the Vita and all would be well. In North America, people would probably jump to tablets and phones. Someone would release a Pokemon clone and life would go on.
They're important, though certainly not essential.
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