We can imagine what sorts of memes have become extinct. Ancient songs that were once sung and never written down are one example. Another example is the many stories that were once told but have since slipped into oblivion. A Story is a vast collection of memes that have come to rely on each other for replication. Such a structure is known as a memeplex.
Stories are memeplexes that are in direct competition with other memeplexes.
If a story replicates through story getting told and read by people, then it will survive. If it stops getting read, it will become extinct. You will see that memes behave in a similar way to genes. Furthermore, you will notice that like genes, memes are subject to selection pressures. Whenever you have a situation that contains a number of unique entities that are competing for limited resources, the entities that are better at reproducing will leave more copies of themselves.