[[Maas]]
Well. You wouldn't find Old High German texts from these areas probably. MHG maybe. But it's you who made the claim that the word died out in all languages but Dutch. Now I don't see how the word can possibly have died out in the dialect of Aachen. That's a pretty daring claim when the river is less than 20 km from this city. So my opinion is that common sense proves that the Aachen dialect has always had a word for a major river less than 20 km from itself. And since (in my definition) it is a dialect of German, the word hasn't died out in German.
But then where are the attestations? Did people not write anything in Aachen until a few centuries ago?
Yeah, you're right of course. One should look for attestations, for example the earliest attestation in a High German text. That has probably been done and I should check it sometime... But I still don't get on what you base your claim. If you say that a word died out in all Germanic languages except one, then I would presuppose that you yourself should have checked these languages for their earliest attestations. You wrote that the German word for "Maas" had died out (or never existed, I don't know). You also wrote that modern German "Maas" is borrowed from Dutch. Now if you say that you need proof, I guess. It's not me who needs to prove the contrary. And of course, if an unfounded claim makes perfect sense then I don't bother at all. (I'm not someone who says we need to quote seven books about something that is common sense.) But this is one thing that just doesn't make much sense to me (personally).-- Best regards, I'm going to bed.