1/ I present the following only because you are curious and this is just my speculation albeit an educated guess. The important facts that we know regarding RBG's pancreatic cancer are: In 2009, she had cancer in distal part of her pancreas that got resected and cured.
2/ In August, they found another cancer in the remaining portion of her pancreas (head/proximal part) for which she received stereotactic radio-ablation ONLY without chemo or surgery, and also she got a biliary stent.
3/ Based on this limited info, it can be deduced that 1) she has at a minimum unresectable or Locally Advanced pancreatic cancer (LAPC), 2) she may or may not have distant metastases (in Jan 2019, they found 2 small malignant lung nodules
4/ that could have been metastases), 3) she got the biliary stent as a palliative/quality of life improvement measure. Now, with that diagnosis, and knowing that she got no chemo after radioablation which only served as tumor debulking,
5/ we can expect her pancreatic cancer (most likely adenocarcinoma; they would have already mentioned the cell type if she had a "better" neuroendocrine type) to be regrowing at the margins of the radioablation.
6/ This regrowth has now led to her most recent hospitalization with sepsis (fever and chills after "stomach bug") most likely caused by obstruction of her biliary stent. As this malignant tumor spreads further,
7/ it would invade adjacent organs such as duodenum, mesenteric neurovasculature (which are probably already involved), stomach, liver and peritoneal cavity. I suspect that she might already be in pain (probably controlled by the likes of opioids that can alter/decrease
8/ her mental capacity) which would only progress. As the adjacent organs get invaded by cancer, symptoms such as abdominal pain and bloating, inability to eat, abdominal distension can follow. Generalized symptoms such as fatigue and psychological issues
9/ such as major depression are quite common in these patients. The median survival for patients with unresectable pancreatic cancer without chemo is probably less than 6 months.
10/ To answer your question of "when will she have to leave" the SCOTUS, I think it depends on how desperate she and her political allies are. I would predict she would be leaving by late Spring or Summer.
