loanwords - Diacritics and non-English letters in anglicized loan words: keep 'em, dump 'em, italicize the words, or what?

Take an expression like déjà vu. This is a French term which is frequently seen in English. In fact, it is included in English dictionaries. But it is often seen in English in a variety of forms:

déjà vu

déjà vu

deja vu

Now, one would probably not consider using frisson or soupçon, both proper unanglicized French words [uh-oh, see edit], without italics to indicate that they were foreign words. But once anglicized, do the words require non-English diacritical marks? Or, if such are used, does that push the word back into foreign status, so that italics are again required?

There's probably a continuum in operation here, during which a word goes from foreign with foreign markings to English with only English markings (or lack thereof). What I want to know is how one can tell where to draw the line. Does anybody have any useful information about this? Guidelines? Or is it on a case-by-case basis?

Honestly, I feel affected writing à la carte when every damn diner you walk into has an "a la carte" (or "ala carte" or "a la cart") category on the menu.

Edit: For example, see the Free Online Dictionary's schizophrenic listing for soupçon:

Soup`con´ n. 1. A suspicion; a suggestion; hence, a very small portion; a taste; as, coffee with a soupçon of brandy; a soupçon of coquetry.

and then in the Thesaurus part:

soupcon - a slight but appreciable amount; "this dish could use a touch of garlic"

So if dictionary entries can't even remain consistent within the same definition, what chance does a mere mortal have?

Answer

I would say that my answer about when to italicize loaned words and phrases is also the most appropriate answer to this question:

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 [have diacritics].

(However, that answer got zero votes, so who knows? I still think it is a good answer.)

Various publications will have strict rules about what diacritics are used and when. For example, The New Yorker always uses diaeresis. Each publication seems to have its own rules for bolding, headers, section numbering, hyphenation, capitalization, reference citation, and so on. And there is no definitive format.

I believe that diacritics fall into this category, as evidenced by their generally inconsistent use (though internally consistent within many publications).