Musical show after worry gets new ending (7)
I believe the answer is:
concert
'musical show' is the definition.
'after worry gets new ending' is the wordplay.
I cannot quite see how this works, but
'after' could be 'once' (I've seen this before) and 'once' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for concert that I've seen before include "Musical event" , "Musical performance" , "Joint action" , "Harmony, performance" , "Some entertainment" .)