Depends of the type of the application. If you have cms application than it cannot be replaced with web (at least some parts) because the application needs to work with local resources like printer, bar code reader, fiscal printer, display and so on.
So, for this type of applications that needs local resources, desktop cannot be replaced.
Also desktop apps can be very faster than web, for cms applications.
Imagine a big supermarket with a lot of customers waiting to pay their orders and paying windows with web applications. I have not seen such thing.
But also there are web frameworks like Oracle ADF that have even more reach than desktop assp.
With ADF you can build web app identical to desktop app, in a way similar to the way the desktop apps are build. But is it expensive, learning curve is high and requires "good" hardware.
But keep in mind that if for web you are not using tested components java script is not so good for mission critical apps, it is error prone.
