UPDATE - we found him!! He was trapped in our neighbour’s yard. We actually had searched the yard earlier today but hadnt spotted him. We were lucky because he had clearly overcome his fear by tonight so wasn’t hiding or silent. We called out to him and walked the neighbourhood with roast chicken once it quieted down, and he called back until we figured out where he was. We had all our lovely neighbours out on their porches trying to spot him in their yards too.
Thank you all so much for sharing and the well wishes! The advice you provided around finding him really worked! And seeing the success stories on the site meant we were able to keep up our hope. Professor is now sleeping totally unphased at home after a big meal and a tonne of water. Our two kittens and the humans in the house haven’t left his side since getting him home.