Ok, so, back at this (was travelling for a bit), and with a nice external drive full of mangled filenames - by the volume of data, there hasn't been much if any loss, and what I don't have in one of two other arrays, I should be able to, erm, rebuild anyway, so it isn't like I'm losing my life's work if I wipe the drive.
Just booted the array up, problematic drive not plugged in. It shows as missing, array stopped, everything looks to be assigned as it should (minus the problem drive obviously), disk prefs set to start with a stopped array.
What's the best course of action from here ? NewConfig, rebuild parity for the good drives and after that add the problematic one as an empty drive ?
(in terms of data rebuilding, the plan is to wait for the screwed drive to come back online, then go read the rsync docs to figure out how not to touch anything that's been added recently to make sure any files that might have been upgraded on the still-good part of the array don't get stepped back to a previous incarnation - I'd assume
du -hs * | sort -h
would still work to, in this case, give me the names of the empty folders, right ?)