He needs 6 more race wins to pass (5 more to equal) Stirling Moss and have more of them than any non-WDC driver.
Only 3 more pole positions to pass Rene Arnoux in PP statistics.
11 more fastest laps to pass Gerhard Berger in FL statistics.
Only 2 points to pass Mark Webber in most points scored statistics. (seems, baring DNF, it will only take one race)
35 podiums to pass Rubens Barrichello in podiums scored (he already has only 34 himself, so that's long way to go here, but it's doable in 2 seasons with Mercedes' current level of speed and reliability)
340 laps led to pas Stirling Moss in laps led statistics.
If Mercedes keep being anywhere as dominant as they're now for the next 1,5 years, Nico will likely overtake all non-WDC drivers in every of those statistics bar podiums and maybe fastest laps by the end of 2016. If he stays in the race-winnig (not necessarily as dominant as current) car for another 2 or 3 years, he has a good chance of building a significant advantage over next non-WDC drivers in most, if not all of mentioned statistics.
Will he find a way to become a WDC to make all of this irrelevant?
If not, I'm curious how will history remember him. Reading opinions on this forum, I don't think most of people would rate Rosberg as good driver as Stirling Moss. But after 10 or 20 years, his actual results may speak louder than people's impressions.
Is Nico not going to became WDC but enjoy significantly more measurable success than any other non-WDC driver in F1 history? How will he be remembered because of that?