For what it is worth, Kerry Vincent freezes fondant covered cakes. I remember her discussion of this on another food-related chat site. She wraps the covered cake, places it in a box, wraps the box several times and then into the freezer.
I’ve never tried this so I cannot vouch for how it works. A lot will depend on the environment - how humid your refrigerator is, how close to temp your freezer stays…. and whether you are using home made fondant or a commercially prepared one.
The longest I’ve kept a fondant covered cake in the cooler is two days. My walk in is humid, and unless the cake is in a heavy duty bag (sheet pan size bags are available to the trade and probably from online paper sources I would guess), the cake will sweat before the day is out. The bag protects that from happening on the cake.
Your mileage will vary. I would definitely suggest testing it out with a small 6” cake to see what happens.
