Ceasing to be built, yes. Gone, hell no.
I was reading an article on the BBC earlier in the week that happened to remark that about two thirds of all Defenders made are still on the roads.
Not sure if the exact figure is true, but my mum and dad owned a small handful over the course of my childhood years in Norfolk. During my time in university, nearly 20 years later, I found one of them in the autotrader (a large green Series II. Fondly nicknamed Ermentrude, after the ease it took to drive). I can well believe that a large fraction of these things will be around for many years to come.