Funny you should ask, @Papergirl1968! Guess who just strolled down the stairs this morning? He ignored me and went first to his bedroom (yes, it is still there and, no, I hadn't redecorated in the two days AlfonosoCat had been gone) and then into the kitchen for breakfast.
He has been shrieking the house down and spending lots of time on my lap being reassured that I still love him and that nothing has changed.
The only thing I can think is that he got out via the master bedroom window when I wasn't looking.