Microsoft (MSFT 1.31%) could release a touch-based version of its Office software suite for Apple's (AAPL 1.97%) iPad before it's released on Microsoft's own Windows tablets, according to plugged-in Microsoft blogger Mary Jo Foley.

If that's the case, Microsoft could be about to deal a crippling blow to its Windows tablets, which have already vastly underperformed Apple's devices. With Office on the iPad, it's difficult to see how Surface and other tablets running Microsoft's operating system survive.

Selling the Surface
Microsoft has run several different TV ads for its Surface tablets, and though they vary significantly, all of them contain the same phrase: "It has Office."

The inclusion of Microsoft Office has been a key selling point for Microsoft's devices, including the Surface and other tablets running the full version of Windows 8. Compared with Apple's iPads, Windows tablets have far fewer apps -- in fact, the Windows app store is so far behind Apple's iTunes, it's difficult to even compare them.

In that regard, it's not surprising that Windows tablets have struggled. Last year, Microsoft took a $900 million writedown on the Surface tablet, after the device sold worse than Microsoft had anticipated. Surface sales have improved but are still nowhere close to the 26 million iPads Apple sold last quarter.

Other companies have tried their hand with Windows-based tablets but haven't found much success, either. Research firm IDC concluded last year that Windows tablets continue to struggle.

Getting rid of its only selling point
Releasing Office on the iPad would shift the balance even more in Apple's favor. Not only can it access a library of hundreds of thousands of iPad-exclusive mobile apps, but it can also run Microsoft's Office. Why would anyone in his right mind still buy the Surface?

They wouldn't. Unless they can't live without a built-in USB port, there simply wouldn't be any reason to purchase Microsoft's tablet over Apple's superior alternative. Although I wouldn't expect Microsoft to explicitly kill the Surface tablet, releasing Office for the iPad would do exactly that.

The Office juggernaut
That said, even if it kills Microsoft's tablet efforts, Office for the iPad could be a boon to the company's shareholders. Last year, Morgan Stanley analysts argued that releasing Office for the iPad could bring in billions of dollars in additional revenue.

There's clearly a demand for Office among iPad owners -- consider all the copycat alternatives that have sprung up on Apple's app store. Even Apple itself, perhaps sensing an opportunity, made its own competitor, iWork, free for iPad owners last year.

Office remains deeply ingrained among corporate workers, making its downfall highly unlikely. Still, the longer Microsoft goes without releasing Office for the iPad, the higher odds become that a true alternative to Office emerges. Given how important Office is to Microsoft (accounting for around a third of its revenue and more than half of its profit), porting it to Apple's iPad seems like the right move for shareholders -- but don't be surprised if Surface doesn't survive.