Surviving former partner beat time (6)
I believe the answer is:
extant
'surviving' is the definition.
(synonyms)
'former partner beat time' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'beat time' becomes 'tant' (I've seen this in other clues).
'ex'+'tant'='EXTANT'
(Other definitions for extant that I've seen before include "Not destroyed or lost" , "Next at being still existing" , "Still existing, not obsolete" , "Still going strong" , "Still around" .)