When a marriage fails, there is no reason for the partners to stay together anymore. They should divorce regardless of whether or not they can or should reasonably expect a second marriage to succeed. It’s not healthy to stay in a dead marriage. In fact, it’s actually a Torah mitzvah for a man to divorce his wife.
Obviously, both partners should try very hard to avoid divorce. They should go to counseling and spend a lot of time communicating to work on their issues. Divorce should be a last resort. But sometimes it just doesn’t work out, and when it’s over, it should be a clean break. No one should stay in a dead marriage for the sake of being married.