There are soooo many variable to consider that I could not hazard a guess. All I can say from experience with my dad's passing this summer (mesothelioma) was it was 2-3 weeks from the time he started refusing food or being able to keep down anything he ate, and about 1 week from refusing to drink more than a sip or two, until that final breath.

The up-and-down roller coaster after he stopped treatment(7 months prior) was really hard for us. He was in and out of the hospital and rehab twice during that period, in serious enough condition (at age 85) that I had already said my goodbyes 3 times.

With his mesothelioma, respiratory issues were the biggest -- constant exhaustion from never getting enough oxygen. With pancreatic cancer, mets to the lungs or ascites in the chest may cause similar symptoms, but you also have to be aware of tumors affecting the spine, nerves, or digestive tract. I would try to get lined up with a good palliative oncologist as soon as possible so you'll know what your options are (nerve blocks, feeding tubes, surgeries) and have an advocate onboard. There's a lot to be said for maximizing whatever quality time you have left while you have it.

I lost two classmates to PC 1.5 years ago. Both in the 58-62 age group and pretty fit. The first lived about a year at Stage-IV with treatment. The second was diagnosed at a gnarly Stage-IV and declined treatment, passing within 3 months of diagnosis, iirc. I wasn't super close to either and not involved in their care, but I did see latter a day before he died, and it was pretty obvious to me the end was very near. 🙁

I'm very sorry to hear you're at this point in your loved one's journey, and sorry I don't have better data or words to convey, but I wish you both the best under the circumstances.