Yes, when I was struggling so with my dd1, I hadn't experienced nursing an older babe or toddler, so even though I was scared and devastated, I had no context for how impactful switching to formula permanently, would be.
That said - if you do end up having a failed challenge when you try to re-initiate, there's always "bottle nursing," which may work well on some levels to help provide that intimacy. My sister who adopted did this with her adopted child (and went on to nurse subsequent children).
What we told ourselves, during the month we were exclusively pumping while giving Ina Neocate, was, "Well, we just need to make it to the end of this month, and see what happens." We set that as a goal and didn't think about what ifs beyond that. If she had failed that reintroduction, I think we would have gone back to Neocate and left it at that (but who knows, maybe I would have kept pumping at least a little, I don't know, it was such a dark dark time for me)..... I do wish I had taken a week off and eaten whatever I wanted at the very beginning of that month - my favorite pizza place closed down while I was on my Elimination Diet.
In terms of how frequently to pump - focus on how much you're getting, if you see a dip, increase duration or timing of it. One of the women I knew while we were going through all our nursing struggles was an EP'er - she had low supply issues initially and worked and worked on it, and by the time her ds was about 10 months of age, she was pumping ONCE a day, and getting 35 oz. !!! Talk about good storage capacity. I do not recommend this - not all women would be able to do that, for certain! I know my supply would tank if I were only pumping once a day! But you may find that you're still able to produce as much with 5-6 pumpings, KWIM?
Good luck with everything.
ETA: I'm really baffled by this -- how weird that there's no blood in the stool with all the other symptoms!? Have you been taking probiotics yourself since this saga began?