fait accompli – to italicize, or not to italicize
Solution 1:
I think this is a case where authors can decide for themselves where to draw the line. Or, if the writing is for a certain publication, the editors will have a policy for whether a given word should or should not be italicized.
Solution 2:
Since fait accompli functions in English as one word, but is written as two, I'd be inclined to keep it italicised. If nothing else, it's a handy hint for anyone who decides to look it up in a dictionary that they should look up the two words together.