I found this short but yet enlightening discussion in the Google Webmaster Help forums about what percentage of inorganic links you need to remove to probably have your inorganic link penalty removed.
An inorganic link is based on a Webmaster Tools notification of a site buying or acquiring links in a none natural fashion. Many webmasters have been receiving them recently and many want to know how to reverse the action.
We know these are manual penalties, at least if you received the webmaster tools notification. So you need to go through the inorganic links and do your best to get them removed.
In the thread, the webmaster said he was able to remove 85% of the inorganic links and asked Google if that was a high enough percentage to submit a reconsideration request and for that request to be satisfied. Google's John Mueller implied yes, it was enough.
John from Google said:
With 85% resolved, it sounds like you've covered a lot of ground already! If there are links that you're absolutely not able to remove, I'd document that with a reconsideration request along with the issues that you've been able to resolve.
So I guess if you can get rid of about 85% of your inorganic links and explain why you can't remove the others, Google might forgive you?
Forum discussion at Google Webmaster Help.
Image credit to BigStockPhoto for % sign