Point about much reduced page is so long (6-3)
I believe the answer is:
toodle-pip
'is so long' is the definition.
(old-fashioned term for goodbye)
'point about much reduced page' is the wordplay.
I cannot really understand how this works, but
'point' could be 'e' (E is an example) and 'e' is located in the answer.
'much' could be 'too' (similar in meaning) and 'too' is located in the answer.
'page' could be 'p' and 'p' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for toodle-pip that I've seen before include "Take care" , "Farewell remark - dipole top (anag)" , "Farewell (informal)" , "Goodbye (dated)" , "so long" .)