Nah. Wikipedia is popular because it is the #1 search result for a lot of stuff. Most of people going there just want to look up something for a homework assignment, online argument, or whatever. If Grokipedia has an error rate 5%, compared to 1% for Wikipedia, it's probably still fine.

If Wikipedia traffic shrinks down just to the true "encyclopedia reader" crowd, they will be in trouble, because I suspect that's less than 10% of their current donations. And Grokipedia is already starting to crop up in search results.