True, it's RNG but that does not mean there's not a way to go around it. Immediately crouching when the map loads while surrounded will let bandits focus on Non-Evil companions, that's cue for newb Lona on Doom mode to dash to the border. Further excursion once Lona level up she can bring smoke bombs or water book...
Though I don't think one should go into Doom mode with just about any build (let alone a level 1 Lona), I think either your default personality Abomination Lona build or that mixed with 20 SCU (sacrifice WIS since Wis only serve 2 functions : to help Lona kill faster and make her summon tougher) is the best to help Lona survive Doom mode.
Lol, if your companions won't help you kill those bandits, they will certainly help you lure them away. That's certainly another way to keep Lona safe in cramped place. But what if those companions weren't there anymore? Like for example, after doing one match in the Arena (which you can only do solo), there would be a moment once you exit the Arena and enter the map where you're going to be accosted by bandits while having no companions. I know there's way to circumvent it but, what I'm trying to get at is that some type of RNG will catch you off-guard one way or another.
As far as Doom mode goes, even if you were planning every moves, there's bound to be some fuck up somewhere that will end the whole run (like me accidentally forgetting to open menu to save and then lose my entire progress after reopening the game, hence why I do Doom save backup) unless you take the really really safe gameplay direction. But as long as you make a backup of your Doom save, I think anything's game. And yes, being stealthy is almost a must (which is why I'm not really much of a fan of Deepone Lona) so having 20 SCU can help heavily in Doom mode since Lona can also get a huge amount of move speed from it (unfortunately this isn't the case in mod like SURVIVOR mod, which is some of the reason I still opt for the highest amount of WIS since there's not only many instances where the SCU is reduced to 0 on this mod, but high WIS also help kill NPCs faster, meaning you conserve more stamina and also kill NPCs in one hit without alerting their backup). As a side note, WIS also increases Lona's Will, which helps when it comes to Succubus build. On top of it, higher WIS will make the damage of blood puddle from Malicious Spore more consistent and reliable, allowing you to effectively and fastly kill lots of neutral NPCs when needed.