Could an executive be given prison time for refusing to testify about what he knew about criminal activity that he was involved in at the company's facilities?

No$,$ under the Fifth Amendment privilege against self$-$incrimination.

No$,$ he cannot be punished for refusing to testify if his testimony could lead to civil charges against him.

Yes. An officer is always liable for crimes committed by a corporation.

Yes. He could be punished because refusing to testify is illegal.