HTML is unlikely to replace native platform development except in some areas where a "cloud based" app makes sense such as calendars, email and file storage... Or in other words where content is document oriented.
The reason is the same as to why Java never replaced C/C++: Performance.
HTML requires runtime interpretation so matter how fast that is made compiled programs will be orders of magnitude faster. The reason lies in the laws of physics and as such will always be an insurmountable factor in favor of machine code.
So called experts have been predicting the end of native programs for many years however it has failed to materialize. When the web catches up and can do something as well as a native program the native program has moved on to even bigger and better things.
There will always be a place for both and the likely future will be just as it is today, a mix of web-based apps and native apps.
As a matter of fact if you look at the current market with mobile platforms included native applications have actually increased.
As a side note, if you are looking at Microsoft as an indicator of the future you will be sorely disappointed. Microsft's "me too" development strategy seved them well in the past however in the last five years it has been their undoing. It is possible that they can turn things around but it certainly won't be with Windows 8.