Guarantees end of strike with nurses working (7)
I believe the answer is:
Here is my best explanation:
'guarantees' is the definition.
('ensure' can be a synonym of 'guarantee')
'end of strike with nurses working' is the subsidiary indication.
'end of' says to take the final letters.
'with' is a charade indicator (letters next to each other).
'working' indicates anagramming the letters.
The final letter of 'strike' is 'e'.
'nurses' is an anagram of 'nsures'.
(Other definitions for ensures that I've seen before include "Warrant", "Guarantees", "Makes safe or certain" and "guarantees".)