Google will send you a formal RMA email and provide a link for you to order your replacement set. Once you do so, you will receive a confirmation email as shown below:
Thank you.
You’ve ordered a replacement from Google Play. The replacement order will appear as an authorization (AUTH) on your credit card but you will not be charged for the device, tax, or shipping, under normal circumstances.
Please check your email for instructions about returning your defective item. Return your defective item promptly to avoid being charged for this order. Please ensure that your shipment arrives at its destination within 21 days from the date of this order to avoid being charged. Following an inspection by the repair service center, the replacement device is yours to keep without charge if the problem is due to an issue covered under warranty.
I hope that answers your question.