Job loss & pre-existing condition questions

I have two events coinciding and am just a little stressed. /s

I may be laid off today. Tomorrow I have a follow up ultrasound after a mammogram.
I don’t know if I should go through with tests or not. If I’m on the cut list I may be able to stay with the company but moved to a much lowering paying job that I would hate. I don’t know if I should do it just to keep insurance on the off chance of bad medical news. I appreciate any guidance kind internet strangers can give with this confusing topic.

Questions:

If I cancel the follow up medical tests now would it still be considered a pre-existing condition? Nothing has been officially diagnosed. However, there is a record of abnormal results and a requested follow up.

If I go through with the test and it’s cancer AND get a new job, would the new health insurance cover me? It’s my understanding that health plans from marketplace cannot exclude pre-existing conditions but does this extend to all plans? If I purchase from marketplace, and have cancer, does anyone know how expensive it would be?