Definition of might-have-been noun from the Oxford Advanced American Dictionary

might-have-been

noun
/ˈmaɪ əv ˌbɪn/
 
[usually plural] (informal)
 
an event or situation that could have happened or that you wish had happened, but that did not happen
Superstar status remained a might-have-been for her.I am not concerned with the might-have-beens but with the facts.