The phrase "unless it happens" is grammatically correct and can be used in written English.
It is typically used to express a condition that must be met in order for something to occur. Example: "I will not go to the party unless it happens on a Saturday." This means that the speaker will only attend the party if it takes place on a Saturday. If it happens on any other day, the speaker will not go.
"You won't find these opinions in any textbook," he says, "unless it happens to be one I've defaced".
As a result, factory reps have fewer retailers to service so there's more attention given to each one than in the past, so the need to travel to a show isn't as great (unless it happens to be local to the retailer).
You can't imagine yourself in that position and what you'd do unless it happens to you.
Unless it happens to you or someone close to you, it goes over people's heads.
For him, localism is meaningless unless it happens to back his personal prejudices.
That is, unless it happens to be doing a little distributed work on the side.
In his ninth novel, Denis Johnson purposefully takes on a slight plot, or what would seem slight, unless it happened to you.
Visits to the hospital or police station warranted immediate notification, but Mom and Dad didn't have to know about less-serious offenses, such as sneaking a six-pack into the dorm, unless it happened more than once.
There is havoc in the market for municipal bonds, though there has not been one notable muni default in at least five years, unless it happened while I was in a deep sleep.
These are clothes that could never be worn to a day job unless it happened to include visiting Anna Wintour with a fashion plan; could never be worn for real-life shopping, lifting of messy children, or any of the other myriad of practical chores/jobs of most women's lives.
And thanks it was an eye-opener for a male.Frankly speaking no male would get it unless it happened to his family member".
