friend who has been happily married to his wife

I have a good friend who has been happily married to his wife for thirty years.

As fate would have it, she met a man she loved many years ago at a class reunion from school, and since that meeting, she started communicating with the man on WhatsApp.

Some time ago the woman asked her husband’s consent to go out with a friend from the past for a long weekend in the desert.

According to her, her childhood friend is terminally ill and she wants to go with him to the desert to have a spiritual experience, exchange memories, and close the circle.

Is her request legitimate and how should my friend respond?