Note: Not a duplicate of Is a refusal to disassociate deleted posts in compliance with the CC BY-SA license?. As its title says, that question has to do with the case where the post involved was already deleted. This has to do with non-deleted posts only.
It's been clear for a while that users who haven't posted very much may have their dissociation requests declined, with a request to delete their account instead.
However, I believe that as contributions to SE sites are under the CC BY-SA 3.0 license, Stack Exchange is legally required to accept all dissociation requests.
I've seen one documented case where a dissociation request was denied; the author later deleted their account, presumably because they were told to do so by the employee who declined the request.
Is this practice legal and within the parameters of the CC BY-SA license? If the user deletes their account, their user ID number will still be attached to it, so it may still identify them and not completely remove the main public attribution as required by the license. (On the other hand, when a post is dissociated, the username is removed entirely and replaced with "anon".)
Or is the "please delete account instead" message not an outright refusal, but rather just an alternate suggestion, and if the user insists on it or cites the license, the request is completed?