That mono shit was a total crap. As wing said, look at Soda, that's what happens if you have mono. You don't play for ages. You do not reach slam finals and semis even if you're Federer, Laver, Sampras or whatever.
No, cut that shit out, that is bullshit reasoning. I got mono my freshman year of college (along with strep the first few weeks), and I was still playing on the USTA junior circuit since I was still 18 at that time. Shit sucked heavily for the first 2 weeks, and for several months I wasn't feeling perfect, but I was still able to pick up several USTA tournaments. Just like ANY sort of issue with the body, it entirely depends on how bad you get it. I know some people who got mono and it was like a mere cold, while some others were bedridden for a hell of a long time.
So just by saying compare to Robin is a really stupid way to gage whether Federer actually got it. I'm not saying Federer truly had it or not, but your reasoning is utter poor for saying he didn't.