Before I lost my Mojo (companion to Xerox for eight years) I was under the assumption that cats just moved on when their owners lost another pet. Xerox is 16 now, and he didn't do that at all. He wandered round the apartment crying piteously until we brought D'arby home. She has claws (he does not) and is almost 15 years younger. I was worried for his safety but at least he quit crying. Since we integrated her into the household the change is amazing.
Yesterday the two of them were rumbling through the apartment chasing each other backwards and forwards, and they barrelled into the living room, D'arby flying under the futon, and Xerox up on top to cut her off on the other side. Well, D'arby flew out the other direction and went back across the apartment to the bedroom, but Xerox can't hear so well these days, and he didn't quite catch that she was already gone. He patrolled the top and eventually went to the end, looked under, and just howled.
I just wanted to tell him she was gone - save him the trouble - but I don't speak Cat. Poor Xero. He got down and eventually took a nap. *sigh*