I will be using a mango curd mixed with american buttercream for a cake and it must be prepared a couple days in advance due to travel time. Am I correct that the cake doesn not need to be refrigerated because of the high sugar/fat content in the buttercream even though it has curd mixed in it? The cake will have gumpaste sugar flowers attached to it and so it cannot be refrigerated. I appreciate your help!

The curd will need to be refrigerated. Buttercream or not.

What if I just use fruit puree mixed in it?

In every case, you have to look at the components and decide if you would leave it out. If you are selling it, the HD will give you guidelines. If they don't know, you must use your best judgement. For example, IMBC has hot sugar poured at 245 degrees. Curd gets nowhere near that hot, probably 180 degrees. The eggs are cooked, but not to the degree of the frosting. If it is for personal use, it's your call.

Because the puree (vs. curd) is free of eggs, you should be fine, especially surrounded by the sugar.

Okay, thanks! I sure do appreciate the feedback!

I refrigerate cakes with gum paste items on them all the time. I've never had any softening problems at all. I use Wilton's pre-made gum paste and it dries very very hard.