Warning message when copying a screen or deleting a component that will cause a screen to lose ‘Available data’
Or perhaps an easier soltion… a red exclamation! next to the screen name in the editor, if it has missing data or is not sending data as it should.
This would be so useful for troubleshooting.
Highlighting the link lines that are causing the problem, or otherwise making inter-page links more visible/distinguishable would speed up troubleshooting too.