According to two Hitwise blog post analyzing the referrers to Yahoo and MSN, they are getting more hits sent from Google than they are getting from their own domain.

http://weblogs.hitwise.com/us-heather-hopkins/2008/07/yahoo_property_breakdown_and_s.html
The following chart shows the share of upstream visits to each of those 20 properties from search.yahoo.com and www.google.com. Most properties receive more traffic from Google than from Yahoo!
http://weblogs.hitwise.com/us-heather-hopkins/upstream%20to%20Yahoo.png

http://weblogs.hitwise.com/us-heather-hopkins/2008/07/msn_property_breakdown_and_gro_1.html
Google accounted for 4.39% of upstream visits to these MSN properties compared to 1.25% from MSN Search and Live and 1.10% from Yahoo! Search.

If there was even a remote chance of Google taking those domains out of the Google organic search, they would stand to lose a substantial amount of traffic

I think the title of this post is inaccurate (or at least it's not a conclusion of the article) . "Most [Yahoo] properties receive more traffic from Google than from Yahoo! Search" is more accurate. This is pretty obvious if you look at Google's market share in the US (comScore/June '08: Google-61.5%, Yahoo-20.9%).