'A decision which a request to intervene and reverse a [bad] Law Lords ruling absolves them from having to decide, surely.'
The remit of the Law Lords was to decide if the extradition request was compliant with our legal system - *NOT* on the facts of the case itself.
The ECHR has to decide if the Law Lords ruling is compliant with the European Convention on Human Rights - at the moment that is still a matter of legal dispute. If the ECHR conclude that the Lords decision contravened one of the principles of the Convention then they will hear the appeal. If they can find no conflict with the Convention then there will be no hearing and the extradition will proceed.