I ave no actual experience of this but done a quick google and found these links which suggest just walking away is not a good solution as you can be presumed in the U.K.. I'm pretty sure nearly all the bank repos on Condado are as a result of the properties being taken from Polaris, not individuals.
https://www.spanishpropertyinsight.com/mortgages-in-spain/problems-paying/
http://www.consumeractiongroup.co.uk/forum/showthread.php?356914-Spanish-Mortgage-what-can-they-do-if-I-stop-paying
Maybe look into the process mentioned in the second link called 'Dacion en pago' which maybe helpful to you. Good luck!