What screen should show after closing an iframe/modal?

I have a challenge of what I should display after a user has triggered an iFrame modal which changes the meaning of the page that it was triggered from.

My assumption is that users would expect a modal is to return to the screen in it's original state after it's closed, but in my case the original screen is redundant after the function within the iFrame is complete.

What would you do to tackle this problem? Turning the iframe into a page is not an option, it must remain a modal.