So it should be simple. The subroutine that gets called with the answers to the previous question closes the old window and creates a new one with new questions. And it provides a new subroutine to the 'Done'- or 'next'-Button of this window.

But think about it. The user would get a sequence of windows that flash "violently" open and close again, probably ignoring where he put previous windows and always going into the foreground even though he might wish otherwise. It doesn't sound like good GUI design to me. Observe other programs on your operating system. How do they do it?

Most will probably have a window that changes its contents to provide the new questions to the user, not generate a new window. Think of install dialogs on windows with those 'next' buttons. Or they will have at most one popup window that leaves the original window intact. Or the window will be successively filled from top to bottom with more and more detail...

By the way, have you noticed how similar the interaction you want is with how web pages work? You press a 'finished' button and the browser tab or window contents is replaced by new information and questions. Also it is easy for a CGI script to create new tabs/windows (but not easy to delete the old ones at the same time, you have to stay in the same tab/window for that). That is another advantage of a web GUI beside the already working client-server communication and the easier graphical design of the GUI