If for some reason you can not get to the pond site to clean up the dead fish what are the issues they would cause besides the strong odor?
I think you'd end up with some serious nastification of your water at a minimum. Plus you could have lots of vermin hanging around and working the dead carcasses, and maybe end up with undesirable creatures living in the area in hopes of more stuff to eat. It just seems pretty obvious that you wouldn't want this set of circumstances to exist.