How to prevent creamy sauces from separating upon reheating?
Is it truly separating? Or is it just that the creamy stuff is sticking like a paste to the noodles, and there is a bunch of oil sitting all by itself at the bottom of the container? 

The latter problem happens to my left over noodles when they have been kept in the fridge for a little while. In addition to the evaporation from the dry refrigerator, the noodles themselves suck up a lot of the moisture from the sauce. The "sauce" becomes a dry-ish paste that can't mix well with the oil. So I add a liberal amt. of water before reheating (trying to keep a gentle touch when mixing it in, so as not to mangle the pasta too bad), and the sauce regains its sauciness. 

Can't imagine what the real chefs would say, but my family enjoys the result.