Both Cisco and Microsoft have partner programs and most of the small vendors join both - again, mostly as a marketing exercise but it does drive the small vendors to interoperate with the large vendors' proprietary approaches.
The open-source community hasn't learned to do bare-knuckle marketing yet. But every time Microsoft has these problems, it helps Linux in a very big way.
They're going to lose market share, that's a given. But I bet they'll still be the market-share leader. They have that brand name, and so far have made acquisitions and aggressive schedules to stay ahead. But they have to execute.