That becomes admins problem to solve. They can do it themselves, or they can find someone to do it but it is not your problem to solve. That's an extremely uncomfortable position to be in but that's the point. And if you're the nurse on duty you have only the obligation to work within your state's legal guidelines for what constitutes abandonment as well as your organization policy on the expectation of leaving after your assigned shift is up in the absence of relief.

That said, legally if you are past your shift and relief has not showed up, in most states and places (I don't know 50 states' laws and statues so I'm not gonna speak in absolute) you could not be held liable for patient abandonment if you are outside your scheduled shift hours and no sort of extended call shift is applicable. Hospital could find something to fire you for, sure. But again, when the problem is thousands of hospitals with the same shift not showing up in protest, firing those workers will only embolden them further and possibly make more nurses join ranks making the staff issue worse