un ‧ pun ‧ ished /ʌnˈpʌnɪʃt/ BrE AmE adjective
[ Word Family: adjective : ↑ punishable , ↑ punishing , ↑ unpunished , ↑ punitive ; verb : ↑ punish ; noun : ↑ punishment ]
go unpunished if someone or something bad they have done goes unpunished, they are not punished:
An attack like that cannot go unpunished.