No, he needs one more world title to equal Eric De Vlaeminck, or two to break the record. Otherwise he'd just be another could-have-been.
He could just do five or six cross-country races next year, but including the World Championship. Or he could skip one year and still break it later, but there's no guarantee he'll still be as good in three years time.
There is a difference between most successful, and best ever. De Vlaeminck may be the most successful in terms of Worlds wins, but I find it difficult to believe he is better than MvdP; Mathieu has raised the bar in what a CX racer is......power, skills/ technique, etc