European visiting revolutionary South American city for so long (7)
I believe the answer is:
cheerio
'so long' is the definition.
('cheerio' can be a synonym of 'so long')
'european visiting revolutionary south american city' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'visiting' is an insertion indicator.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'south american city' becomes 'rio' (I've seen this before).
'e' inserted inside 'che' is 'chee'.
'chee'+'rio'='CHEERIO'
'for' acts as a link.
(Other definitions for cheerio that I've seen before include "Informal goodbye, sounds blithe" , "Bye" , "Ta-ta" , "Bye-bye" , "Say this before drinking" .)