回複：offer is gone

Don't expect the hiring manager would do any favor for you. He/she would not put themself in a position agaist HR. This is exactly what had happened on me. I received the offer letter, signed and mailed it back. Several days later they terminated the offer due to my visa transfer hassle. I contacted the hiring manager who agreed to speak with HR. I know for fact that he did try however he knew nothing about H1-B. It is so easy for HR to persude him. I called him several time and left messages. I have not heard from them ever since. I was told later by HR that the position was filled...
Well, it is reality. Anyway, treat it as compliment. You will have other opportunities. You will be more confident. This is exactly what I feel now.