How do you handle a seller backing out 2 days before closing?

Had a seller go dark 48 hours before our scheduled close last week. Title was clear, EMD was deposited, buyer was ready to fund. I tried calling, texting, emailing — nothing.

What's your playbook for this? Do you send a notice of default? Try one last in-person visit? Walk away? I want to hear what's actually worked for people.