Glottal stops and the status of the London (UK) Cockney dialect

I am sorry to ask such an apparently off-topic question, but what is
the status of the London (UK) Cockney dialect? The question arises
because the Cockney pronunciation of `t' between vowels is widely
used in language textbooks to explain how to pronounce the glottal
stop; this example will become invalid if standard English via the
public media obliterates Cockney along with all other English
regional dialects.