OK, found it.
The mod causing a crash whenever a non-protag character gets killed (grey portrait) and ~ 1 round passes is Artemius' House Tweaks.
The only components installed from it were:
~HOUSETWEAKS/HOUSETWEAKS.TP2~ #0 #2 // House Tweaks: Expanded Racial Bonuses: 1.91 ~HOUSETWEAKS/HOUSETWEAKS.TP2~ #0 #7 // House Tweaks: Increased Constitution Bonuses -> Constitution Bonuses for All Classes + Regeneration Changes: 1.91 ~HOUSETWEAKS/HOUSETWEAKS.TP2~ #0 #10 // House Tweaks: INT/WIS/CHA-based Bonus Spell Slots: 1.91 ~HOUSETWEAKS/HOUSETWEAKS.TP2~ #0 #12 // House Tweaks: Improved Dialogues (BG:EE )1.91
Each one installed by itself also caused the same crash (edit actually both Increased Constitution and Improved Dialogues do NOT result in a crash, either separately installed or installed together).
However, I am only about half-way through this process. I got the crashes with this and a couple other mods installed ahead of it, namely 3 kits from the same author (Artisan's Kitpack), Dan_P 's Blood Minister kit, Avenger's Wizard Slayer kit, Tweaks Anthology, Tome & Blood, JMerry's Tweaks, 3 of the Made In Heaven mods (all save for Tweaks), AC's Miscellaneous, and some of 'Reddbane's 3.5 Edition/Pathfinder style Tweaks. Obviously not every component of every mod was installed but NONE of those mods resulted in a crash before House Rules was added.
Right now I'm going to reinstall with ONLY the House Tweaks to isolate the behavior. Will post more shortly.