I had an AF ticket issued by DL for an CDG to Stuttgart flight last Friday. My meeting got cancelled, so I called DL to fly home from CDG instead and they re-issued that ticket and cancelled the Stuttgart ticket for full credit. I think the answer is to always make sure you have a DL issued ticket not an AF issued ticket.
They did try the "you can't use this lounge" bit until she noticed my ticket said Elite and I was holding my CR card. This was in the 2C biz lounge. The Delta person re-issuing my ticket told me that 2E would re-open for check-in soon and would have a bus area on the airside to take you to the flights while they knock down the old airside part that collapsed and rebuild. Hopefully the new louge was in an area not being knocked down and rebuilt.