Its interesting to look at their matchup in stages, at least by the statistical record.
2004 - Roland Garros, 2006: 6-1 Rafa
We tend to think of Rafa's overwhelming dominance being more recent, but its important to remember that he totally had Roger's number for the first 2+ years. It was as if Roger didn't know what hit him. Amazingly enough, this was also when Rafa was mostly a teenager and Roger was at the height of his powers.
2006 Wimbledon - 2007: 5-2 Roger
Return of the Jedi? Roger re-balanced things, figured out how to play the young bull so that through 2007--Roger's last year of true dominance over the tour--the matchup was close at 8-6. I'd also say this is the last phase in which Roger was in his ultimate peak.
2008 - 2012: 10-4 Rafa
Rafa's rise to his peak in 2008, with Roger losing a half step led to a pretty one-sided affair. Rafa dominated but the matches were still interesting and Roger managed to win a few of them.
2013 - present: 5-0 Rafa
Rafa has utterly dominated Roger in recent years, although this is perhaps partially due to Roger's collapse in 2013. Still, its hard to imagine Roger beating Rafa again, as age is also a factor and even if Rafa starts slipping out of his absolute peak form, he'll be a lot closer to it than Roger. Still, if Roger is serving out of his mind and/or they play on grass, we could see a nice throwback to one of their classic Wimbledon matches.