Kid in heap on the way out (8)
I believe the answer is:
moribund
'on the way out' is the definition.
(I've seen this in another clue)
'kid in heap' is the wordplay.
'kid' becomes 'rib' (both can mean to tease or mock).
'in' indicates putting letters inside.
'heap' becomes 'mound' (synonyms).
'rib' inserted within 'mound' is 'MORIBUND'.
(Other definitions for moribund that I've seen before include "At death's door" , "Near to death" , "About to die" , "not quite dead" , "In a dying state" .)