If you don't reply, or if the buyer isn't satisfied with the outcome by 12. Jan. 2015, the buyer can escalate the case to eBay Customer Support. Learn more about responding to a request on eBay.de.
In the meantime, PayPal funds from this transaction, including payment and shipping, will be unavailable for withdrawal. However, you can still use these funds to send a refund the buyer. How to refund the buyer