Hi monks, I want to use a Tk window to ask a user a question inside a function, and then return their answer as the return value.

This is thinking "procedurally" rather than "event driven". In an event driven framework, you would simply put up a new widget somewhere with your question (perhaps in a different window, but not necessarily), and then exit your handler. Assign a callback to the "I'm done" button to trigger a new event to handle what had formerly been the second half of your subroutine.