Well, the existence of Google Docs in the office, of Chromebooks in schools, of AWS controlling a large share of what MS lusts after, etc indicate to me that perhaps they aren't destined to remained the dominant force they once were, similar to IBM.

Now, I know Microsoft is a near-2-trillion-dollar company, but they would not be the first company to have realized the folly of resting on their laurels.

Microsoft's future over the 20 year term doesn't look as rosy as it could. They'll remain a huge company, but perhaps they'll slip back into the hundreds-of-billions-of-dollars segment instead of the trillion-dollar-titan segment if the investments they're making don't pay off.

They'll have huge income for decades because it's costly and time-consuming to move away from existing systems, but for new companies, Microsoft is no longer a given.

Microsoft is not sliding into irrelevance, they have been growing quite significantly precisely because they have not been resting. Azure is their primary focus, and it's now on the verge of becoming the largest cloud provider.