Elephant Watcher agrees that Perry's debate performances have lowered his odds of winning the nomination while raising Romney's odds. Prior to the debates, Elephant Watcher's calculation of the odds had 18% for Romney and 16% for Perry; it is now 22% for Romney and 12% for Perry.
But even if Perry does not win the nomination, it is unlikely that he will collapse completely. He may still have a significant impact on the race, especially in Iowa and South Carolina. Perry remains as a significant obstacle to any other potential Anti-Romney candidate. Rick Santorum and Herman Cain have both been touted by anti-Romney commentators as potential replacements. They will need to get past Perry first, and he will not make it easy.
Despite his disastrous debate performances, Perry is still famously skilled at the so-called "retail politics" that occurs in the early primary states: Face-to-face meetings with individuals and small groups. Perry is well-funded. At least for now, Perry rivals even Romney when it comes to his "political machine." Despite the new concerns about Perry's electability, he is still considered more electable than Cain or Michele Bachmann; Santorum remains an unknown.
It's also possible that Perry can rehabilitate his image in future debates. On the one hand, Perry's poor performances in all three debates indicate that he is simply bad at debating. This may not change. But that doesn't mean Perry cannot improve. His campaign almost certainly realizes that his future depends on improving in debates. That should force Perry to focus. Expectations for Perry are so low now that any improvement may be seen as a positive, even if Perry is not outstanding. If he fails to shoot himself in the foot at the next debate, his campaign will undoubtedly hail him as "the comeback kid" and attempt to push a "redemption" narrative in the media.
If another candidate wishes to replace Perry as the chief Anti-Romney figure, he must convincingly lead Perry in the polls for awhile. Only then will Perry's numbers crash and support coalesce around Perry's replacement.