More than anything else, the decision on Office for iOS and Android will show Microsoft's long-term strategic direction, said O'Donnell, who knows what he'd do if he ran the company.
"They have to decide what's more important, Office or Windows," O'Donnell said. "The operating system battle is a lot harder for Microsoft to fight than the office productivity battle, so if I'm Ballmer, I would put more of my bets on Office."
By the estimate of rival research firm Forrester, Microsoft's monopoly of the OS market -- 95% as recently as 2008 -- has evaporated, hitting a low of 35% in 2012 as smartphone and tablet sales exploded.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is email@example.com.
Read more about mobile apps in Computerworld's Mobile Apps Topic Center.