Whatever the situation that led to a late or missing shipment, it’s your responsibility as a seller to make it right.
Here’s the good news.
Buyers can only escalate an Item Not Received (INR) case to eBay after 3 business days. Those 3 days begin from the moment a buyer contacts you to check on their parcel status. So, if the INR case is opened on the 12th, they can only escalate it on the 16th. They can’t speed up this time frame. Meaning, they can’t escalate a complaint earlier than 3 business days after the INR case is opened.
So you have that three days grace period to make it right by your buyers. Important note: The 3 business day SMIR period is based on the calendar of your listing site - ie. US, UK, AU or DE. Please be mindful of the time difference and any public holidays when you are handling late shipments.