I actually think what Shinoj says makes a lot of sense.
Ahahahaha, of course you do.
Anyway to answer the actual thread question, I think by 2013 the Fedal era will basically be over and they'd have to almost fluke another Slam victory. I don't think there's so much winning left in Federer, and slightly more in Nadal.
To address a couple of other things:
Wodger had a clear decline starting from 2008 due to mono probably and it coincided with a increased emergence of Nadal, and then Nadal and Fed ruled the roost jointly from rg 2008 - AO 2010 in roughly equal proportions but by this point (2009) as a tennis player Fed was certainly aging. I reckon Fed's prime was 2004 - 2009 but he was setback in 2008 due to mono, and from 2010 onward clearly demonstrated both a physical and mental decline compared to his best years, the signs of which I started seeing in a more permanent sense around US Open 2009 AO 2010 period -- Well he has an awful lot of matches under his legs so it's certainly understandable.
Also, to suggest that Nadal and Djokovic are better adapted to the current conditions is reasonable, certainly in the context of an aging Federer, but I think even if he was prime-time then he still might not be better equipped than Nadal and Djokovic to deal with the current conditions in tennis.