So, for no particular reason I decided to build my first character without putting a single point in any weapon skills; the goal was to beat the game without personally ending a life. Also no destroying any robots, no squishing any bugs, nothing that would trigger 'Enemy Killed'. That went for companions too. Sending robots back to their charging pods or putting enemies to sleep was allowable, however.
The end result? A pretty big success, in fact. The main quest did not require me to actually kill anyone, and I was able to complete the vast majority of sidequests. There are points where killing might seem inevitable, such as the radio tower; but they are ultimately avoidable.
Since I saw some other people interested in a 'pacifist run', I thought some might be interested what exactly you can and can't do, as well as what they'd need to pull it off. First, some tips:
What you need to know
In Fallout: New Vegas you had relatively little control over the companion AI; if you had them with you, they would shoot. It's important to realise that this isn't the case in The Outer Worlds: companions can be set into 'Passive' mode, which will prevent them from attacking under any circumstances unless specifically ordered to. This is good; companions provide massive buffs to your skills, so for a no-kill run they can be very important failsafes.
To put it in perspective, by bringing SAM and Max along I was able to boost my Intimidate by 43 points, while still providing large boosts to Hack and Science. They're useful. Inspiration and Determination, though, are largely irrelevant beyond the level 60 Inspiration perk; double the skill boost from companions, which is very enticing, but maybe not worth the investment. I am unsure whether it applies to the Companion Perks that boost your skills further while a companion is in the party.
It's also important to have a good understanding of the stealth system. Since you can't access terminals while in combat, it's generally going to be important to stay in stealth -- even ignoring that if seen people'll shoot at you. You can, however, still pick up items and leave/enter areas in combat, so the running wildly approach is sometimes an option.
So: crouching in tall grass makes you virtually invisible, and inside you'll want to make good use of cover and enemy patrols to make your way through areas. You'd be surprised by the amount of back and alternate entrances; if going in through the front seems impossible, it's not a bad idea to scout around. Hacking/Lockpicking will open up routes and potentially save you from having to scour areas/bodies for keys.
What quests I couldn't do
What you think you might not be able to do, but can
What I didn't do, but you probably can
What I did, but you might disagree with
The marauders at the start of the game, near your ship? They don't need to be dealt with, not even by talking the guards into fighting them; you can just stealth past them. ADA's fake-venting stunt will scare them away, as the two Spacer's Choice people will tell you.
If you put out a fake tracking signal for Phineas, I wouldn't count it against the run but he'll kill a few people having prepared his defenses, which Sophia will wave in your face. I don't actually know if you lock yourself off anything by sending a real signal; and of course, if siding with Phineas you probably don't have to send anything at all.
To my knowledge, Nyoka's companion quest cannot be completed; fortunately, everyone else's can be finished.
Every quest I was able to complete by location, to my best recollection