go under

to sink:
The ship went under just minutes after the last passenger had been rescued.

If a company goes under, it fails financially:
The charity will go under unless a generous donor can be found within the next few months.

informal
If a company goes under, it is unsuccessful and has to stop doing business:
Thousands of companies went under during the recession.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの go under の定義 © Cambridge University Press)

アメリカ英語辞典
(of a business) to fail financially:
Nothing could be done to keep the bank from going under.
(Cambridge Academic Content Dictionary からの go under の定義 © Cambridge University Press)

ビジネス英語
if a company goes under, it becomes bankrupt:
The company will go under unless new financing can be put in place soon.
(Cambridge ビジネス英語辞典 からの go under の定義 © Cambridge University Press)

- Cambridge Dictionary