Split up the business and go separate ways (4,7)
I believe the answer is:
part company
'go separate ways' is the definition.
(thesaurus)
'split up the business' is the wordplay.
'split up' becomes 'part' (synonyms).
'the business' becomes 'company' (company is a kind of business).
'part'+'company'='PART COMPANY'
'and' acts as a link.
(Other definitions for part company that I've seen before include "Not all of the rep actors" , "Separate" , "leave" , "Split up" , "Break up" .)