In regards to the cheese whipped with confectioner's sugar: Try this trick to save it:

scrape the contents of the bowl into another container, then wash and completely dry the bowl. Return it to the mixer with a few tablepoons of butter/ or nondairy butter. Whip at high speed. Add the broken mixture one heaping spoonful at a time. Don't add the next spoonful until the one before it has been incorporated.

This should return it back from the dark side. Stop a few spoonfuls shy of adding the whole mixture or it might break again. I learned this trick for saving broken frosting from the amazing pastry chef (and my mentor) Pichet Ong.

Kristen Miglore, our senior editor, wrote in a post on whipped cream: "Salvaging extremely overwhipped cream can be done. Add up to 1/4 cup of cold whipping cream and work it in, stirring with a rubber spatula to restore the proper consistency."

So I imagine this goes the same for mascarpone cheese "whipped" with confectioner's sugar and vanilla beans which was supposed to be a topping for a cake? It quickly separated into butter solid and liquid. Sad... it doesn't even taste that good as butter. Should I add bit of salt?

What do you mean by "broke?" Did it separate and turn buttery? If so, sadly, no, you can't salvage it as whipped cream. But you can scrape it all into a colander lined with a couple of layers of cheesecloth, press it gently and let the "buttermilk" drain off, and call it sweet butter. And then there is the adage, "If at first you don't succeed, erase all evidence of having tried."