The goo and ash piles in vanilla need one tweak from the original version.
A Script on the ash and goo piles with On Load block with a counter which disabled and marks them for delete.
They vanish every time with this.
Once I got this into a mod, I went back to killing stuff with lasers, plasma, and alien weapons.
Enemys still respawn with this, even the Talon Company mercs I ashed

SCN SomeScriptNameScriptShort TimesBegin OnLoad Set Times to Times + 1 If Times >= 2 Disable MarkForDelete EndIfEnd