Artist to leave, before returning forever (4)
I believe the answer is:
goya
'artist' is the definition.
(Francisco Goya)
'leave before returning forever' is the wordplay.
'leave' becomes 'go'.
'before' says to put letters next to each other.
'returning' says the letters should be written backwards.
'forever' becomes 'ay' (historic term for 'forever').
'ay' reversed gives 'ya'.
'go'+'ya'='GOYA'
'to' acts as a link.
(Other definitions for goya that I've seen before include "Francisco de ---- (1746-1828), Spanish painter of portraits" , "Old master" , "Portrait painter" , "He painted Wellington" , "his etchings?" .)