Wired headphones will never really go away, sort of like optical drives have never gone away despite the fact you now need the external drive and the adapter to run one (yet Apple sells both). There will be adapters, but I expect them to remain more of a mainstream product than the optical drive, which is much more a niche product anymore. (I have an older program for Windows which requires a CD, so I still use the USB SuperDrive and run it virtually on the Mac; otherwise, I probably would have never bought one).
There are also those who just prefer the wired headphone, and I'm one of them. I'm a runner and have had my wired earbuds come out plenty of times on a windy day, so I don't really want something without a failsafe wire. They're also just easier to keep together, not to mention I've got tons of sets of them from all the iPhones and iPods I've bought over the years (and even an extra pair from the time I forgot them on a trip and bought a set at the Baltimore airport). I also don't want the inconvenience of having to charge one more thing--I have enough adapters between the laptops, iPhone, iPod, iPad, digital camera, camcorder, and a TI-84 calculator I use as a teaching tool (yup, they're rechargeable now too).
Still, don't forget Apple currently has the iPod touch still on the price list. It's a great little music player, perfect for when you need to free up an iPhone for something else or don't want your music rudely interrupted by the automated spam caller trying to sell you an extended car warranty despite being on the "do not call" list; it also (most importantly, to me) saves on the phone battery and makes it easier to use on a run for actually tracking the run.
Floppy disks were made obsolete by their storage limits. Optical drives have largely gone away as well. Headphones will always be around because they can continue to improve, rather than be constrained by the limits of old tech.
Similarly, the iPhone camera hasn't stopped some of us from still using Nikons despite the fact the iPhone camera is fine for a quick snapshot or even a slightly better photo.