On reflection, gang needs to accept bereavement to flourish (7)
I believe the answer is:
blossom
'flourish' is the definition.
(I've seen this in another clue)
'on reflection gang needs to accept bereavement' is the wordplay.
'on reflection' says the letters should be written in reverse.
'gang' becomes 'mob' (synonyms).
'needs to accept' means one lot of letters goes inside another.
'bereavement' becomes 'loss' (I've seen this in another clue).
'mob' in reverse letter order is 'bom'.
'bom' placed around 'loss' is 'BLOSSOM'.
'to' is the link.
(Other definitions for blossom that I've seen before include "Flower - flourish" , "Flowers on a tree/bush" , "Flowers on, eg, cherry" , "Do well" , "Come into flower" .)