Harsh about replacing author's final piece (7)
I believe the answer is:
austere
'harsh' is the definition.
(I've seen this before)
'about replacing author's final piece' is the wordplay.
I cannot quite understand how this works, but
'about' could be 're' (common abbreviation for 'with reference to') and 're' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for austere that I've seen before include "Abstemious and grave" , "Severe or strict in attitude" , "Severe, lacking comforts" , "Stern or very plain" , "Lacking adornments" .)