Please add details and clarify the problem being solved.
(This is an injoke about some site boilerplate text. Hang around a while, you'll see it eventually if you haven't already.)
One of the functions of the domain knowledge that an expert should possess is to be able to distinguish the meaningful and meaningless elements of the relationships between things in that domain.
This is why the question page asks you to be specific and provide details. If things have come to the point that you hope anonymous strangers on the Internet will be able to solve your problem, you should be honest with yourself that you are, at least situationally, not an expert, and you do not know how meaningful some of the details of your specific situation are -- so provide as many as you can. Be open, be conversational, tell your story! (Well, not the personally identifiable details of your story. This is the Internet, after all.) If some of it turns out not to matter, or to be a distraction from the more relevant elements of your question, you can edit it out later -- regardless of site reputation you can always edit your own stuff freely.
I understand the impulse to pull back into generalities to hope for something useful by chance, but if you need specific help, asking more and more general questions trying to find it is only likely to get you more and more general answers.
Especially in this case, wow! I mean -- you probably already know this, but I'm writing this just as much for a general audience -- Call of Cthulhu has been going for over 40 years now, and over most of that time it's built up something of a reputation as a real investigator meatgrinder. The seventh edition of Call of Cthulhu (CoC7E) is written in what I would, uncharitably, describe as a defensive crouch against its own reputation. "Don't kill the investigators! Don't kill the investigators!" it's screaming, left and right.
Don't kill the investigators... in general.
Where possible try to avoid an outcome that will end the game (unless you wish to, of course).
-- "Failed Dice Rolls and Sudden Endings", CoC7E Keeper Rulebook, p. 86
It's just fine to kill them in specific. Like, when the story's reached its climax and even their deaths would still be interesting.
And hey, while I'm copping to being uncharitable! In what an outside observer would probably call a thoroughly predictable plot element, as this whole affair has dragged on I spent way too much time in close reading of that eldritch tome and it messed with my head a little. I've done jack all to help you get to this point and my responses to your more and more general queries have made the whole thing worse for you.
So: thanks for putting yourself through the process and opening up about what you were trying to do. I'm sorry for the confusion you've been through, both personally induced and in general. If you want to head back to your original question and edit in all these details you've shared - the final confrontation, the dire threat, the desperate escape - I can absolutely get you a better answer.