Seriously depends on his new work options which depends on the job, his location and his age.
I took voluntary redundancy 5 yrs ago, got a nice lump but that's it, once JB runs out then means testing means you get nothing if you have savings. I have not managed to find a new job other than a couple of short term things since, but I am in small town Ireland and am over 50 which is the kiss of death for getting a new job in my opinion based on my experiences.
I have many days when I regret it, even though I know if I had stayed they would have found a way to get rid of me as they have done many of my former colleagues, we weren't wanted so it's hard to battle against that.
So basically if he is sure he can get another job, that to me would be the main decider (having said that I was sure I would too!)