Just thinking loud.
So if Raila was to face Mudavadi in a run-off what will it mean? Going by the possible facts I believe this is the most dangerous scenario for Raila. First consider this; Mudavadi will get the state backing while Rail wont. this is true from the almost open backing he is getting from President Kibaki - reading his speeches and representing him in public functions. secondly Mudavadi will get the central backing because of his good blood with Kibaki. Obviously Kibaki has his followers in the central waiting for his word. A word that will definitely be in favor of Mudavadi.
One can also say that Mudavadi will get a fair part of Rift valley votes due to Raila's act of dumping and messing up Ruto. Obviously there are the few individuals who see Raila as a Judas to the Kalenjin which to some level is understandable. Mudavadi will also get a good vote number from Western because of 'his people' voting trend that has been in Kenya since time immemorial. Mudavadi's kith and and kin can never disown him for a 'shemeji'. Also not to forget is the fact that ODM - Raila- had promised the Luhyia a backing after the 2007 elections. That is a political debt that the Luhyia are still so aware of.
Nairobi votes as usual don't belong to anyone. As a metropolitan it has a fair representation of both Luhyia, Kikuyu, Luos and other tribes so here the shares will be evenly divided. So as Raila boosts of Kibera, Mudavadi will be boosting of Kangemi and Dagoreti.
Moving to coast; Raila has a command of the people, they love him as he helped in having the Sheria law as part of the constitution. But the problem is Raila has just lost Mombasa votes to MRC since they wont vote. 'Pwani si Kenya' and as much as this seems like a minor issues, our Muslim brothers are so good at listening and following they religious leaders as long as they can relate their ideas to the Holy Book.
Now lets consider a case where Uhuru, Ruto, Wamalwa, etc fail to make it to teh run-off. Definitely they would rather back Mudavadi than Raila. Remember as the trend up to now is that each candidate's manifesto is not to increase youth employment, or to expand the economy but to stop Raila. And I trust their bid comes from the heart.
There are also high chances Raila might not choose Kosgei as a running mate since he is KANU blooded something that Raila's right hand men wont welcome easily. So if this happens, he will have lost some of the Rift Valley votes plus a backing of the Big Old Men in the run-off. So while Raila is still in his comfort zone, and Mudavadi is working his popularity, his men should wake up and brace for a real war since Messi is now very ready and armed.