but because i'm covering the cake in fondant, i was wondering if the mousse would hold up if it wasnt refrigerated. Can fondant be refrigerated? Or should I come up with a different filling?

I refrigerate all my cakes, fondant and all. It's only a problem with condensation if it's warm and humid out. I find that refrigerating the fondant covered cakes help keep it firm. I also think that the mousse filling will get too soft.

A perishable filling must be refrigerated!

If you choose not to refrigerate fondant covered cakes, then you need to limit the choice of fillings to those which are shelf stable.

HTH

Fondant can be refrigerated. Combine that with Jan's important warning, and as she said you have two ways to go with this: find a shelf-stable mousse recipe (it will be a "mock" chocolate mousse basically. Depending on where you live Rich's Bettercreme would be a good option) or simply refrigerate the cake, fondant and all. I've had better luck refrigerating commercial fondant or Michele Foster's recipe, rather than straight MMF. Although MacsMom refrigerates her MMF...but she adds glycerine to the recipe.

i have a big cake this week. chocolate cake from scratch filed with mousse. I will refrigerate it, will the cake remain moist as it has butter? if served at room temperature, the cake will be good but filling might get melted, how long the fillings like this can remain outside?

Thanks.