When I was in London I had a big huge B&W visit me every night and wanted to move in, I put up posters and his owners were on holiday as Rosella has said and he didnt like the person coming to feed him, so left.
I found out that he tried to move in next door too and I saw him in his home, flaked out on the sofa after his humans came home.
He visited me every night until I moved, was a long time.
I hope that you are able to trace the owners down, its unlikely they would chip and then leave the cat to fend for itself I think.