A feared scenario almost always plays as a freeze-frame: the film runs up to the worst moment - the job lost, the news delivered, the words said out loud - and stops there, as if the projector burned out and that frame is now the permanent state of the world. The fear never shows you 11am the next day, because at 11am the next day you are visibly coping, and coping is bad for the fear's business.
So write the film past the frame. Let the worst thing happen on the page - fully, without softening it - and then keep the pen moving into what fear never shows: the next morning, with its coffee and its phone calls. The first week, with its logistics. The people who would appear - write their actual names - and the things you would actually do, because you would do things; you always have. Then the next month, and the next year, by which point the page usually contains something the freeze-frame could never contain: a life, altered and continuing.
Then write the plan in cold blood, as if for someone else: if this happens, here is step one, step two, who I call, what I can spare, what I'd let go. A catastrophe with a plan attached is demoted to a problem - a large one, maybe, but problems have edges, and it is the edgelessness that was keeping you up. Finish with one honest line about the odds. Feared things are usually both less likely than 3am believes and more survivable than the freeze-frame shows, and it takes writing to catch both at once.
One boundary, said plainly: this theme is for the circling "what if", not for a real emergency already in the room - a real emergency needs real help, not an essay. And when the feared thing eventually doesn't happen, take it to the graveyard of worries next door. It will be in good company; that ground is full.