The term is a fad. The group of people themselves have always been a reality.
You have to remember that this is a label they gave themselves - "involuntarily celibate" shortened to "incel". 100 years ago, the random incels would be isolated cases, they would fade into irrelevance or change. Now, thanks to the internet, they can bond together through their misery. They neither fade away because they now have an in-group nor do they change because they have fellow incels telling them that their experience is not their fault, it's happening to others.
The term is appearing everywhere because these incels are yet another vocal social minority that uses the internet to amplify their social presence beyond their actual numbers. The media picks up on them because we've had some very sensationalist crimes committed by people who share their opinions, such as that guy Elliot Rodger.
They're not going anywhere, although the term they self-refer by might change.