Plagiarism can no longer survive in its entirety. It is very difficult to be entirely original. Copying word for word is a high possibility because many people think in similar ways because of media influence.
As far as stories go, I think every possibility of every story has been told. Many stories of the past, the present real or not and a multitude of variations of the future from science fiction to ridiculous with a heavy dose of creative licence and wonders have been done.
Plagiarism in music is one area which fascinates me because how easy it is to tune a piece which at some point has been done. It could be at a different beat but tunes can have a familiar ring to it.
I think plagiarism was probably needed in times when creativity was being created but I think to monitor it, is very difficult. We hum tunes and find a creative side but sometimes the tunes we hum are made up of music around us and to stumble into plagiarism is very easy.
I think when we create regardless if it is written stories, music or anything else worth the creative juices then just write with passion. Don’t worry if it borders on copying particularly if you are innocent of the intention.
Writing releases the stories inside of us, it releases the creativity of the moment so don’t let plagiarism spoil the art.