name is guaranteed to be constant. So is site_url*.
Use one of them.
/users/{id}/associated is not vectorized (as a part of stackauth and not api.* it doesn't follow the "all {id}'s are vectors" rule) and thus you should be able to keep track of that information yourself easily.
*There might be some goofiness with area51 created sites in this regard, we'll keep you posted when the details shake out.