About 5 years ago, I spontaneously experienced acute pancreatitis (not sure why), but fortunately, I was already in the hospital for a foot surgery. Anyway... my pancreas hemorrhaged, and I was rushed down to the Intensive Care Unit (ICU), and I received several blood transfusions. I believe three in all. The doctors said I lost a lot of blood -- about the maximum needed for me to stay alive, and it was a miracle they detected the hemorrhaging when they did. So how much blood might I have lost?
That depends on the age and general condition of the patient, as well as why and how fast and where they're losing blood.
In your case, if you had pancreatitis severe enough to perforate the splenic artery (or another of the many large vessels touching the pancreas), the answer is "not much, cause you're already in bad shape". Then again, if that were the case, you'd have most likely been in the ICU before the hemorrhage happened for treatment of severe pancreatitis, and would have required surgery or interventional radiology to fix the bleeding, and the transfusion requirement would have been higher than three units, because blood loss quickly rises to litres from a major vessel like that.
The other option is known as hemorrhagic pancreatitis in which you bleed into the tissue of the pancreas itself. It doesn't necessary mean you'd end up needing surgery, and if you did, it would not have been for bleeding, it'd have been to clean out the dead parts of the pancreas. In such a case, blood loss would not be severe (minimal, in fact), but coupled with the rest of the stuff that goes very very wrong during pancreatitis, you'd have needed a modest transfusion anyway, in order to keep your blood hemoglobin content optimal, rather than just good enough (we don't usually transfuse to optimal, because the benefit of that is usually nowhere near as large as the risks of the transfusion itself, so we settle for good enough, if possible).