I think Obi-Wan would have forgiven Anakin right up to the point that he was talking with Padme before he strangled her. I think if she had talked sense into him and he had repented and told Obi-Wan he'd go kill the Emporer with him, Obi-Wan would have agreed. He was searchign for any way to forgive him. Once he strangled Padme, Obi-Wan knew he was gone. You wish it wnet the other way, but then we'd have no black mask and it'd be over.
Am I overanalyzing? Probably, but I don't care!