Is it okay to stay in a marriage for the sake of the kids even though you are unhappy.?

Ok so I just wanted to know what you guys think about this. I personally am stuck in the middle. My fiance's parents are getting a divorce after 22 years of marriage. His dad filed for divorce about a year after my fiance's youngest sister graduated from high school. My fiance says that he always knew that his dad stayed in the marriage just for him and his siblings. He says his parents always put on a happy smile in front of him and his sibling, but were very quiet and distant towards each other. However his sister says that she is glad that her father stayed because she needed him, and she wouldn't be the person she is today had they split up, and didn't have him in her day-to-day life. So I was wondering has anyone else been in this situation or witnessed their parents in this situation.