Remains in party after leader goes (3)
I believe the answer is:
ash
'remains' is the definition.
(I've seen this before)
'party after leader goes' is the wordplay.
'party' becomes 'bash' (term for a party or celebration).
'after leader goes' means to remove the first letter.
'bash' with its initial letter taken away is 'ASH'.
'in' is the link.
(Other definitions for ash that I've seen before include "Remains of conflagration" , "Common tree" , "remains after forest fire?" , "Volcanic dust" , "Tree; burnt residue" .)