Peg out wearing gold for so long (5)
I believe the answer is:
adieu
'so long' is the definition.
(both can mean goodbye)
'peg out wearing gold' is the wordplay.
'peg out' becomes 'die'.
'wearing' means one lot of letters goes inside another.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'die' inserted inside 'au' is 'ADIEU'.
'for' is the link.
(Other definitions for adieu that I've seen before include "All the best" , "the last word in France" , "Goodbye, madame" , "farewell message" , "Gallic goodbye" .)