Half decide to return. See snobby leader coming around, so formally withdraws (7)
I believe the answer is:
secedes
'formally withdraws' is the definition.
(I've seen this in another clue)
'half decide to return see' is the wordplay.
'half' means to take half the letters.
'decide' becomes 'seal' (sealing is a kind of deciding).
'to return see' becomes 'cedes' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'seal' cut in half is 'se'.
'se'+'cedes'='SECEDES'
'snobby leader coming around so' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for secedes that I've seen before include "Breaks away" , "makes a withdrawal" , "Withdraws from an organization" .)