Died: duty nurse being replaced by junior (10)
I believe the answer is:
understudy
'junior' is the definition.
'died duty nurse being replaced' is the wordplay.
'died' becomes 'd'.
'being replaced' indicates anagramming the letters.
'd'+'duty'+'nurse'='ddutynurse'
'ddutynurse' is an anagram of 'UNDERSTUDY'.
'by' is the link.
(Other definitions for understudy that I've seen before include "emergency role" , "Replacement" , "One prepared to take over from leading actor" , "one's hoping to get on" , "Stage stand-in" .)