What is a mid life crisis for a man like for his wife?

Depends. People change and the relationships in which they involve change with them. In pop talk, a midlife crisis is a decision to change one's focus in life for greater fulfillment, realizing one's time is limited. If this involves setting and achieving worthwhile goals, maybe the wife will be happy. If it involves philandering, she has my sympathy and may have her own priorities change as well.