I suspect that Google has some kind of internal metric for the quality of its data sources, based on the integrity if the data they find there. As time goes on with Yahoo not giving owners a chance to change and update their data, they're going to end up with hundreds of thousands of incorrect live listings, and you know that Google sees that. I have nothing to base this on, but I strongly suspect that Google's already got Yahoo weighted as being a bad directory with poor quality data. Do your best to be thorough when doing your citation work, but at the end of the day... the less able you are to change it, the less likely it was super important anyway. I'm surprised to see a big name like Yahoo! Local go down the tube like this, but just because it's a big name doesn't mean it's exempt from dropping the ball in Google's eyes. If anyone does have a good solution, then by all means do it... but in the meantime, an hour more spent beating your head against this here is going to be far less productive than an hour spent on the huge pile of other local SEO work I know you've got for the client. 80/20 rule and all that.