It's already completely destroyed by the time they've departed to catch kitten (10)
I believe the answer is:
eradicated
'it's already completely destroyed' is the definition.
I can't tell whether this defines the answer.
'by the time they've departed to catch kitten' is the wordplay.
I cannot really see how this works, but
'by' could be 'at' and 'at' is found in the answer.
'time' could be 'era' (an era is a period of time) and 'era' is found in the answer.
The remaining letters 'diced' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eradicated that I've seen before include "Completely eliminated" , "Completely removed" , "Completely destroyed" , "Wiped out" , "annihilated" .)