It's hard to compete against an incumbent, even when you offer a massively superior product and have a huge marketing budget to promote it.
In markets where there was no incumbent influence, linux has generally beaten microsoft hands down.
Linux will never conquer the corporate desktop as it currently exists, but what is far more likely to happen is that the desktop becomes a small niche for specific use cases while the mass market moves on to web based applications that can be accessed from any device. For these uses android devices are already well suited.
As for the remaining desktop niche, microsoft may decide that it's not worth their time to serve a much smaller less profitable market and pull out altogether.