Another possibility is that he regains his old job. I've seen that happen recently - guy left our org for a hotshot startup in a different domain, politics happened and his position was essentially rendered unviable. He rejoined our group and didn't lose status or reputation for his 1 month stint.

At least this guy didn't get hired before that happened. IMHO he's dodged a bullet. If he was good with his old place they'd probably be good to hire him back.