First off, Nintendo would invent something to replace him if Mario couldn't be used for some imaginary reason all of the sudden (lawsuit, lack of popularity, protesting his 'stereotype').
Second of all, if Mario had never been made in the first place, Nintendo, and gaming as a whole, would be a lot smaller than it is today. So on that note, its like asking if Squaresoft could have survived without Final Fantasy or Sega without Sonic. Which ironically I guess my examples aren't too good since they both required buy outs from other companies....
In the end, I'd say Nintendo would have done fine. However, Mario was the plateu that pushed them over from a modreately successful arcade publishing company with a struggling home console to one of the most successful game developers ever.
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