Microsoft is definitely going to be around in 10-20 years, if only because of the captive audience that is their enterprise customers. The large corporations made huge investments in training, customized software, and back-end support for Microsoft Windows, and Office. Heck, there's no real alternative to Outlook for businesses, and Excel/Powerpoint are industry standards at this point. Moving to another operation system or office suite will require back end changes, and retraining their IT staff and employees, and Microsoft has moved quickly to fix all the fuckups with Windows 8, which was a stupid attempt to grab up the consumer market for commodity products.
Enterprises are okay with paying the Microsoft tax because they are more concerned about long-term support. You can always find someone who can provide technical support for Microsoft server products, but it's harder for Linux.
In sum, Microsoft just needs to be "good enough" for its enterprise customers to stay with their solutions. Microsoft has been playing the "follow the follower" strategy that game theorists suggest that market leaders should be doingâ"when you have a large lead, you shouldn't innovate. Rather, you should let people with smaller market shares bear the burden of innovation, and when they succeed, you follow them. That's what has been called "embrace and extend" but you don't embrace dead ends. That's why you see Microsoft getting into business cloud solutions (Office 365) to compete with Google Apps.
Also, Microsoft will only get stronger as Intel's mobile processors get more powerful. You already have tablets running Windows 8. Within five years, you will see smartphones running full versions of Windows.