And if he doesn’t show up? What are they going to do? Refer him to the DOJ?
Yes, refer him for criminal prosecution for defying a Congressional subpoena. They may not prosecute him, but he’ll then have that asterisk associated with him forever, like a few others.
They also have the rarely used but not unprecedented option of involving the House’s Sargeant at Arms/police force, which has its own jail under the Capitol.