I finished the game in Low Chaos and am now going to do High Chaos. Is it possible to do High Chaos run while sparing the main targets?
I don't have tested it BUT:
I've played a run#1 with FULL Low Chaos: 0 kill 0 detection 0 alert on Main game + 2 DLCs
I've played a run#2 with FULL High Chaos: 0 kill 0 detection 0 alert on Main game + 2 DLCs
For the High Chaos run I've done a part you want to do, let me explain:
I've killed ALL the militaries
I've killed ALL the weepers (they don't count neither as civilians or "militaries" but still as ennemies)
I've killed ALL the MAIN targets -> And YOU want to save'em ALL
Bad actions I've done which increase High Chaos:
High Overseer Campbell: Poison Slackjaw's still for Granny Rags side quest
High Overseer Campbell: Save Geoff Curnow from Thaddeus Campbell's assassination attempt (nb: he is a military) -> PERHAPS you want to save him
Lady Boyle's Last Party: Kill Lord Montgomery Shaw -> PERHAPS you want to save him
Return to the Tower: Kill the Royal Interrogator -> PERHAPS you want to save him
The Loyalists: I've killed all ennemies so I don't have to use the Arc Pylon
A Captain of Industry (DLC#1): Destroy the Rothwild Slaughterhouse
Eminent Domain (DLC#1): Kill General Turnbull
Good Actions I've done which decrease High Chaos:
High Overseer Campbell: Save Overseer Berthold and his sister from Overseers (nb: even if Berthold is a military, his sister is a civilian)
The Royal Physician: Rescue the woman trapped from a swarm of rats in an abandoned factory on the north side of Kaldwin's Bridge (woman civilian)
The Royal Physician: Release Anton Sokolov's test subject 312 from confinement (woman civilian)
The Flooded District: Save all the plague survivors ("Blake and co") in Creating a Safe Haven (all civilian)
A Stay of Execution for Lizzy (DLC#2): I've maintained Overseer disguise which result escaping with no evidence behind
A Stay of Execution for Lizzy (DLC#2): Stop the Execution of the Guard who helped Corvo in the main story (even if he's a military, he helped you. Plus 2 civilians with him.)
The Dead Eels (DLC#2): I've restored the water to the canal counting as a good action BUT it doesn't count because I've killed the doctor before
Informations for High Chaos:
Note that all informations above should count for medium chaos.
Medium Chaos means you killed more than 20% of ppl and less than 50%.
Moreover "Medium Chaos" remains a High Chaos State !
Finally as a "pure High Chaos" way, normally the moment your TOTAL kills exceed 50% of the whole population the city is irrevocably thrown into chaos.
Note the population amount rises choosing the darkest way (i.e. LC-Medium-HC)
But ... I've read this is NOT an absolute treshold amount cuz of all "good actions" described above + the main characters spared or not.
That being said I've not done the exact path you want; I do believe yours will be quite the same exept you want to spare all the MCs.
Btw I'm quite sure killing ALL ennemies (militaries + weepers) should lead to HC path even sparing the MCs, thus let us know !