1.) A joint venture won't happen, much as there will never be an
agreement between Yahoo and Google. If yahoo gives up only it's search
business, it won't have a means to generate any significant revenue.
That won't happen!
2.) A full buy-out of Yahoo by Microsoft is the most likely senario!
It would be bad for Google initially from a perception stand-point,
but Google will not lose anything to those two, so Google will bounce
right back!
3.) Google's third party advertising platform is the only way that
Yahoo and Google will get together, but anyone can now advertise as a
third party (if approved), so it will just mean more revenue for
Google. Google wins!
In any case, Google still dominates!