I was going to mention downgrading again and starting over in the first place but I had a similar issue just the other day. i was stuck in recovery and even tried installing the downgrader pup in recovery and got stuck at 99%. it booted back in recovery. in the end I tried rebuilding file system and it got stuck at preparing so i unplugged it. Turned it back on and it proceeded with rebuilding the file system. I thought i was screwed for sure.
Anyway, sorry about the loss.