What is your title implying? That Federer's last year is 2013? It will be hard for him to drop to 5 to 8 when he is making grand slam semis on average. Ferrer won 7 titles last year and still could not break into the top 4 that year even with Nadal out for so long.
It amazes me, the absolutist nature of tennis fandom statements on these forums. There are lots of rounds played in a match, momentum shifts, mental gaffes, etc. Federer has the experience/intangibles to pull off a 7-6 set win while playing crappy, as we saw multiple times yesterday. Yet somehow a tough five-set loss against the younger player in a semifinal means he will never win a slam again.
Federer would have won no slams after 2008 and Nadal none after 2009 if they had mindsets like yours.