Company must replace leader of organisation -- that's the law! (12)
I believe the answer is:
constitution
'the law' is the definition.
(constitution is a kind of law)
'company must replace leader of organisation' is the wordplay.
I cannot quite see how this works, but
'company' could be 'co' (abbreviation) and 'co' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
This explanation may well be incorrect...
'that's' is the link.
Can you help me to learn more?
(Other definitions for constitution that I've seen before include "make-up" , "(Person's) general state of health" , "legal system" , "Body of principles governing a state" , "set of rules and regulations" .)