What if Microsoft just walked away from the unsolicited bid it has made for Yahoo?

What if, indeed?

That’s a new concept that I have been hearing more frequently over the last several days from sources in Silicon Valley and Wall Street.

Let’s be clear: The software giant’s hostile offer for the troubled Internet portal seems to have remained firm, even after Yahoo rejected its $31-a-share bid (worth less now, as Microsoft’s stock price has dropped) on Monday.

“As we have said previously, Microsoft reserves the right to pursue all necessary steps to ensure that Yahoo!’s shareholders are provided with the opportunity to realize the value inherent in our proposal,” said Microsoft in a statement. “Based on conversations with stakeholders of both companies, we are confident that moving forward promptly to consummate a transaction is in the best interests of all parties.”

But what if it is not in the best interests of Microsoft?

And what are the other options Microsoft might have that are actually better than scooping up Yahoo, especially to serve its Captain-Ahab obsession with harpooning the Great White Whale of Google?

If that is the actual goal, then many point out that a Yahoo win does not really frighten Google all that much, since the search giant has done just fine competing against both already.

In addition, many noted that a union of the pair, which would distract both Yahoo and Microsoft, might not be the magic bullet needed to fell Google from its high perch. And then what?

One idea I have heard, for example, was that Microsoft take its $44.6 billion in cash and stock it plans on spending on Yahoo and go on a shopping spree of the Web 2.0 companies all around Silicon Valley and all over.

And not just a few–lots and lots of them. And, more than one person suggested, it should start with Facebook, even at that wacky $15 billion valuation that Microsoft itself validated when it invested $240 million in the social-networking site recently.

“So what if it is only worth $10 billion or even less,” said one person. “They could lose a lot more on the risk of buying Yahoo.”

With the $30 billion left over, it could be like Christmas in July for the geeks and venture firms of Silicon Valley. But Microsoft could scoop up a lot of good stuff, even if prices are high.

Here’s a list: LinkedIn. Digg. Flixster. Slide or RockYou. Veoh. WordPress. Sphere. Sugar. Some international stuff. And more.

Then, some noted, Microsoft would have to give massive financial incentives to those entrepreneurs to stay and thrive. Most importantly, it would have to keep its Redmond hands from interfering.

Now that would send shivers up the spine of Larry and Sergey.

More importantly, it would be forward-leaning, instead of how Benchmark VC Michael Eisenberg characterized Microsoft in a recent post on his Six Kids and a Full Time Job blog about the deal: “Microsoft, in my opinion, has a tendency to look at others’ mistakes and then chase yesterday.”

Chasing yesterday is a bit of a harsh analysis of Microsoft’s efforts to win Yahoo, but it also has a definitive ring of the truth.

In any case, if Microsoft did walk away, Yahoo’s shares would likely plummet back to low levels, unless the company found a quick way to revive its business before some other suitor came knocking.

And, who’s to say that that suitor couldn’t be Microsoft again?

What if?

And for your viewing pleasure, here’s the faboo Nancy Sinatra singing one of my favorite songs of all time for no good reason, “These Boots Are Made for Walking”: