Well, "can no longer play online" isn't really the story? Plenty of us are still playing online, including with the Origin-delivered Battlefield 1942, using one of the "after GameSpy shutdown" solutions that are listed here. Many players and servers still online.
I have wondered what would happen if I entered in my physical CD-ROM key into Origin /now/, after Battlefield 1942 has been removed from the Origin store.
Entering in your Battlefield 1942 "legacy" CD-ROM key into Origin /before/ Battlefield 1942 was removed from the Origin store would actually add Battlefield 1942 to your My Games, same as if it was a purchased product activation key.
But I already did that /before/ Battlefield 1942 was removed from the Origin store, so Battlefield 1942 is already listed in My Games with the "legacy" CD-ROM key. I'm unable to easily test what happens if you do those same steps /now/, unless I create a clean throw-away Origin account and use a different "legacy" CD-ROM key.
If it still authorized you to add Battlefield 1942 game to your My Games (since Origin does still have Battlefield 1942 available for download; you just have to "already own it", and can't purchase it or get it for free from the Origin store), that could be a useful option for players who have a damaged physical CD and could use the Origin-delivered Battlefield 1942 instead.
-Trench