Many will drop by the wayside, it's true, but many will catch on, be used more, and finally win out.
Variety is the key to language change.
Vocabulary is probably the most unstable. Slang, of course, is particularly fickle. Teen slang has a strong American slant, of course. For slang to be slangy it has to startle, and above all it has to be new. Sounds are constantly on the move.