Like a magician who knows he has one last rabbit up his sleeve, he delivers his famous keynotes with a twinkle in his eye. Even if you are pretty sure what his “one more thing” is going to be — and you are never 100% certain — he makes you wait for it.

Which is why the suspense surrounding Macworld Expo 2009 — the last in which the company will participate — is so palpable.

When Apple PR announced on Dec. 16 that senior vice president Phil Schiller — not Jobs — would be delivering the keynote next Tuesday, the news set off an orgy of speculative thumb-sucking.

Hundreds of TV spots, newspaper articles, wire stories and blog posts chewed over the possibilities. Was Apple feuding with IDG World Expo — the company that has been putting on the exposition since 1985? Was it simply pulling the plug on a show whose time had passed? Were there no new showcase Apple products worthy of a Steve Jobs keynote? Was there a last-minute glitch in a new piece of hardware? Could it be that Jobs had lost more weight or was too sick to appear? Had his pancreatic cancer returned? Was his health “declining rapidly” — as one thinly sourced rumor had it? Was he, as others insist on not much more evidence, just fine? Or is it all, as still another faction firmly believes, nobody’s business but Steve’s?

Apple’s December surprise may have lowered expectations for Macworld 2009 in terms of product introductions, but it only raised expectations in terms of Apple’s CEO — because it didn’t rule out the possibility that the rabbit in Schiller’s sleeve next week is …

… wait for it …

… Steve Jobs himself, making a cameo appearance just before the curtain falls.

The beauty of this scenario is its simplicity. There are only two possibilities: either Jobs shows up or he doesn’t.

If he does, and looks no worse than he did at the Spotlight on Notebooks special event in October, the audience will erupt with applause,  investors will be reassured, and Apple’s (AAPL) share price will soar. When Jobs made a surprise telephone appearance at Apple’s fourth quarter earnings call three months ago, the stock jumped more than 12% in after-hours trading.

If he doesn’t show, things get a bit more complicated.

Few CEO are more closely associated with the health of a major company than Steve Jobs, who not only co-founded Apple in 1976, but brought it back from near bankruptcy when he returned from exile 20 years later.

Today Apple is both a worldwide leader in high-tech innovation and a financial powerhouse with a market cap of $75 billion, annual sales of $32 billion, and $24.5 billion in cash.

Two years ago, when the company was  caught up in an options backdating scandal, Piper Jaffray’s Gene Munster estimated that if Jobs were forced out, Apple’s shares might drop 20% overnight. How big a hit it will take when Jobs leaves — as he eventually must do — remains to be seen.

Some argue that Jobs’ departure has already been priced into the stock; after all, it’s fallen nearly 60% since its Dec. 2007 high of just under $200 a share. (It closed on New Year’s eve at $85.35.) One theory has it that Jobs is skipping Macworld now, while the stock is low and cash reserves are high, because he has already decided to step down.

One thing is certain: If he doesn’t show up next week, or at the World Wide Developer’s Conference in June, or at whatever special events Apple schedules in 2009, then it will be clear that the transition to the new management team is already underway, and the era of Apple’s Steve Jobs is nearly over.

UPDATE: For a perspective on Macworld keynotes as they appear to insiders at One Infinite Loop, see Chuq von Rospach’s piece in Friday’s Guardian.

[Photo courtesy of Matthew Yohe.]