Hi, I've only made a few fondant cakes at this point and I get nervous about what will keep for a few days with out refrigeration. Should I stick with all shortening, no milk butter cream? I really prefer the taste of 50/50 shortening and butter, but I don't know if this would be a safe option since the cake will be sitting on my counter for a few days. Any other suggestions for fillings that don't have to be refrigerated would be appreciated!
Thanks!!!

Your 50/50 recipe should be fine left out at room temperature. The high sugar to dairy ratio acts like a preservative for the final product. I used a 50/50 buttercream recipe on my cakes for years and I never refrigerated them unless they had a filling that needed refrigeration.

The only reason I ever refrigerate mine is to get it cold so I can apply the fondant, and if I fill with something I don't want to spring a leak, then I fridge or if it can spoil...never worried about my bc, I use butter and shortening and coffee creamer

That's great to know, thanks so much!!!

Butter itself does not require refrigeration, buttercream is fine out at room temp.