Sauce – Making a sauce with mascarpone cheese

Yes, that should be fine, but bear in mind that cream cheese has a sharper, subtle cheese taste whereas mascarpone is more or less triple cream, and thus milder. If you want that sharp taste, perhaps add just a little lemon juice with your mascarpone.

Cheese is a cultured product, so you should follow the advice in the question:

How do you know when a cultured item is no longer safe to consume?

Since it's been acidified and (if it's store bought) probably also pasteurized, it's very unlikely that any harmful bacteria would be able to compete with the "good" bacteria. Most cheese never go bad in this way - they just go sour, rancid and/or grow mold.

Which means that if it looks fine and smells fine and tastes fine, it should still be safe to eat.

Cheese is essentially preserved milk; it was originally intended to be stored at room temperature (before refrigeration existed), it just keeps its quality longer in the fridge.