This legislation came into force in last month and I have been discussing it with our board f governors and the LEA.
As a list...
a) Holidays or absences booked (with proof) before parents were aware of the rule change are classed as exceptional. This is the view taken by our local group of schools and endorsed by our LEA.
b) A blanket ban on holidays would be contrary to the intent of the legislation.
c) The legislation uses the word exceptional, the interpretation of this word is for the head.
d) If you consider the width of meaning of the word exceptional, you can see why there is latitude in interpretation: "Being an exception; uncommon." "not usual : unusual or uncommon".
e) Even if the absence were unauthorised, a fine does not automatically follow.
f) The head has to ask the LEA to fine the parents.
If I was the OP, I would write a letter stating all the facts and go to the wedding.
In my school, this absence would be authorised.