The world would be a much sadder, drearier place without the 555. That's the nostalgia part out of the way.

Really it's such a useful almost universal lego block of a component that it's hard to imagine it going away anytime soon. Sure microcontrollers are as cheap as chips these days, but you get a lot more with them. Do I need to say that sometimes more is less? Can think of scenarios where you absolutely don't want to see a chip containing firmware/code which needs auditing and locking down.