This is the same niche I fell into - building applications to standardize the work happening parallel to SAP because it didn't cover the edge cases, and people created their own workflows using mostly spreadsheets passed around. Which, comically, our client eventually bought another enterprise piece of software to cover our niche. We figured the gig was up...that was 5 years ago. Turns out the new enterprise software covers only a tiny fraction of the edge cases, so ours just keeps chugging along, paying the bills.