Even if 10,000 people report a single post, that post will only yield one warning for the account owner, and only if Instagram finds that the post violates their Community Guidelines or Terms of Service. Instagram’s algorithms also automatically detect posts that violate their policies and issue warnings to those account owners—an account can receive a warning without a human ever reporting the post! You can check your warnings in the Instagram app—on your profile, tap the menu at the top-right, tap Settings, select Help, and then chose Support Requests. Any warnings you’ve received appear in the Violations area.
Unfortunately, there’s no way to know how many warnings one needs to receive before their account is deleted.