Perhaps ASCII itself is to blame, but in my experience the first two spellings you list are less widely used than "fiance" and "cafe", respectively.

I wouldn't base a paper on it, but (fiancé versus fiance): https://books.google.com/ngrams/graph?content=fianc%C3%A9%2C...

café versus cafe: https://books.google.com/ngrams/graph?content=caf%C3%A9%2Cca...

I argue "Bēowulf" is does not fall under "widely used." Even my high school version of it it was printed "Beowulf." I'm not claiming "ASCII contains all characters used at all in English," just refuting the claim that you can't "write proper English" with ASCII and that it is missing "widely used" characters.