There has been some reporting over the past few years of there being little evidence in the genetic record of the current population* for massive population change as a result of the Anglo-Saxon invasions, and speculation that the change may have been more of a 'top of society' one backed up by cultural/ fashion changes that make people who were Romano British look Anglo Saxon. Anyway...
I like to think that the sudden absence of pots after about 500 AD is not because people had forgotten how to make them, so much as a change in cooking habits.
Let's face it, ceramics are a bit of a pain as storage. One bump and the damn things break (as I was reminded this morning when Kjetil chucked one of my flowerpots down the steps). And if you were using them for cooking, that would happen a *lot*. It did. That's why there is so incredibly much Roman pottery all over the place.
So, maybe people decided that actually, casseroles and stews and slow pot-cooked things are not that great, and became enthusiasts of fast-cooked food.
I like to think of the people of Dark Age Britain as enthusiastic spit-roasters and barbecuers. People who were excellent wood carvers would use nicely turned wooden bowls and platters that don't fall to bits the first time you drop the damn things. I bet they used a lot of woven baskets and intricately made platters as well - just look at the remaining metalwork, you can see these are people who really like to weave and wind things!
They would use wooden spits, perhaps kebab-style, or maybe there would be a treasured metal spit that was rolled out for cooking whole animals, in the manner of a village lamb-roast (am not sure if AS metalworking would be able to make something unbendy/unsnappy enough to do that or not... Maybe the thing to do would be a wooden spit with a sort of metal cuff on each end to protect it from the fire. ) Or maybe they would have useful iron grills, which when they finally died would be recycled into other objects...
I bet they were a lot warmer in their snug wooden houses than chilly people in stone buildings. Have you lived in a stone building? Brrrrrr! You have to build them insanely thick to keep the warmth in and even then the floors are chilly. Whereas the upstairs of our house is single-skin wood and it's *warm*.
In fact, generally, I like to think of the Dark Ages as a period of clever use of wood technology, now sadly lost to us as the Normans burnt a lot of it and the rest has rotted away. I have no idea if this is true, but I'm pretty sure nobody can disprove it!
* I don't quite understand how they can tell what genes are from Chepstow and which ones are from Saxony, given that people have presumably been moving about between the 2 and having sex like bunnies ever since, but I assume there is some way or someone would have pointed it out by now. Probably.