If the holders of the UEFA Europa League have already qualified for Europe, no extra domestic place will be gained.
http://www.premierleague.com/en-gb/news/features/european-competition-qualification.html
Which means only 5th will get a Europa League spot. Swansea City from the Leaque Cup, and 1 from the 5 teams left in the FA Cup.
Yeah, but what if Chelsea finish 5th and win the FA Cup, and the runners up have qualified for the Champions League?