Dining implement, the last piece. Finished! PS Never to be disposed of (3,5)
I believe the answer is:
for keeps
'dining implement the last' is the definition.
I can't tell whether this defines the answer.
'piece finished ps never to be disposed of' is the wordplay.
'piece' becomes 'r' (abbreviation for Rook).
'finished ps never' becomes 'keeps' (I can't justify this - if you can you should give a lot more credence to this answer).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'be disposed' indicates an anagram.
'of' is an anagram of 'fo'.
'r'+'keeps'='rkeeps'
'rkeeps' put after 'fo' is 'FOR KEEPS'.
Can you help me to learn more?
(Other definitions for for keeps that I've seen before include "in favour of strongholds" , "indefinitely" , "Always" , "Permanently (colloq.)" , "with serious intent" .)