Yanukovych's better bet might to be get enough defections from the current Timoshenko led MPs to switch over to support a coalition led by the Party of Regions. Back on Feb 3 when Ukraine’s parliament approved changes to the election law three days before the final round of the presidential election which was opposed by Timoshenko is already a sign that she can longer command a real majority. Now that Yanukovych seems to have won will make that pull even greater. I reckon that the reason why Timoshenko has not cried fraud yet given how close the election was is that she wants to made a deal with Yanukovych where she stays on as PM. She will threaten to undermine the result if she does not get her way. I suspect Yanukovych will call her bluff by breaking her party with defections and her demonstrations will most likely fizzle out given the disunity between the Yushchenko and Timoshenko in the old Orange coalition.
Now that Yanukovych has won, you might get new parliamentary elections or Yanukovych manages to get a PR majority in Parliament (probably through the support of the Communists and Lytvyn's party - the latter of which is now in the Tymoshenko government).
