Enduring Heather, having drunk endless wine (7)
I believe the answer is:
lasting
'enduring' is the definition.
('lasting' can be similar in meaning to 'enduring')
'heather having drunk endless wine' is the wordplay.
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
'having drunk' is an insertion indicator.
'endless' means to remove the last letter.
'wine' becomes 'asti' (I've seen this before).
'asti' with its last letter removed is 'ast'.
'ling' placed around 'ast' is 'LASTING'.
(Other definitions for lasting that I've seen before include "Abiding, durable" , "long-term" , "there for long while" , "Persistent" , "Evergreen" .)