One more thing that may need doing in that modification, if a monster death is required to trigger something to enable advancement. To be safe I should probably make sure that code like the last few lines of monster_death_use gets invoked for all the ghosts (and then maybe NOT do that part of monster_death_use when it actually dies). Will get back to poking around at that soon.
Edit: E4M7 is a nice test case (the vores at the end). Made a couple of changes so that that map is completable.
Edit 2: Checked that all maps are completable.