Happen to get separated (4,3)
I believe the answer is:
come off
'happen' is the definition.
(coming off is a kind of happening)
'get separated' is the wordplay.
'get' becomes 'come' (coming is a kind of getting**).
'separated' becomes 'off'.
'come'+'off'='COME-OFF'
'to' acts as a link.
(Other definitions for come off that I've seen before include "Be removed; turn out; succeed" , "don't stay at peak" .)