So, Conservative only quietens rebels after one leaves (12)
I believe the answer is:
consequently
'so' is the definition.
('consequently' can be a synonym of 'so')
'conservative only quietens rebels after one leaves' is the wordplay.
I cannot really see how this works, but
'conservative' could be 'con' (I've seen this in other clues) and 'con' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for consequently that I've seen before include "As a result" , "thus?" .)