Starch and gum? I'd have thought there would need to be gluten or some other kind of protein in there. Shows you what I know.
Once I've woken up a bit more, I'll post my hot & sour soup recipe. It does involve an egg, and I'm skeptical of how well egg replacer would work in this case. But I have an idea for a replacement. Let me cogitate on this a bit while I make another pot of tea....