A speaker, in essence, is still a piece of wire electrically, so odds are good there's a break. It could also be that the cone the electromagnet coil is attached to is damaged in a way that it can no longer make sound, but odds are better that a connection is broken - for example one of the flexible ones that run directly to the coil.
It could be that it shook loose with use or if overvoltage burned out a turn in the coil.... doesn't really look like there are additional electronics in your headphones, but something in there could be damaged if it exists. Also worth changing to a different source - maybe the output has failed in that it works normally but can source very little current, so it can't effectively drive a load as significant as headphones.