I've been having a lot of discussion about this with my brother, actually.
A lot of translations give out a set of cues to us, the reader, that they are using "archaic language", or other strategies, to say "this was a long time ago, and this is the image I want you to have in your head."
But the problem is that, like the music you hear every time Romans show up in film and television, they're in no way accurate to what things were actually like. They're just a set of cues that have been set up by more modern media, and our exposure to has told us that "those french horns mean Romans". We've been attempting to translate Beowulf into our perception of medieval speech as run through an academic English professor's verbiage. Considering that it was the sort of thing to be told around the drinking table, and was written down in that way, translations like that make very little sense.
Basically, we're already not translating "faithfully", and arguably haven't been since shortly after the poem was written down (if the original was even totally faithful, to begin with, but that gets into a whole other set of questions). This is a fundamental issue with translation, and especially translation of poetry - translate literally, or tell the story, or meet in the middle somewhere. they are two finite points that cannot both be satisfied fully. Headley herself weighs in on this in her preface, which is worth the cost of admission in and of itself without the translation.
If this gets dated, the correct response isn't to go back to the old translations (save for reference), it's to translate it again. And again. It's got to live, and it's got to be in the vernacular if it's truly going to be relevant and not left to the dusty corners of libraries and the drudgery of English Lit curriculum. Indeed, I'd pay money to get even the first two dozen lines or so written in as many common vernaculars as possible. Army guys around a table, steelworkers on lunch break, the Tuesday night sewing group, the activist group at a meeting, and so on.
The story is in the telling, after all.