> If you kill one of Ediff's vital buffers, then try to leave Ediff (by
 > typing q in the control window), there is an error.
 >
 > The error is:
 > ediff-visible-region: You have killed a vital Ediff buffer---you must leave
 > Ediff now!

'y-or-n-p' mangles 'this-command'.  Something like the attached patch
should fix that.

martin