Update. Yes, he's back, half an ounce or so lighter but really doesn't seem to care that his chances of fatherhood are now gone forever. He's running around like a mad thing chasing a feather I got for him, and stuffing his face with any food he can find.
And Paws is happy to have him back. He's sniffed and licked Oliver all over and let Oliver eat from his dish, which is practically unheard of!