Wow, that sucks majorly.
I was hoping it wasn't back! I have absolutely NO experience with demodex at all. But why is the vet waiting to do bloodwork? At this point, I feel like they might as well just do it now. And bloodwork is recommended to be done yearly anyways, so you could make sure everything else is functioning properly as well. I don't know, just my non-professional thoughts. Has he ever had bloodwork before? It just seems like it may not be a bad idea at this point in time, as it won't be a total waste, even if it doesn't pinpoint the demodex problem he's having. I think that would be the step I would be taking now, but like I said, no experience with any kind of skin infections, mites, etc. Demodex is a form of mange, right?