This service/application only provides visual design. What happens when the boss says "okay, now show me where the users sign up and edit their profile"? Are you going to say "But we can do animations with Google Web Designer!"?

This "replaces" web design (hence the name) not web _development_.

The appearence of typewriters was not the end for book writers. It gave a better and more comfortable tool to do their creative work.

If you think your work is not creative, and all you do are very simple and automatic things that become trivial with this tool, then yes, that work could be in danger.

As far as I can tell from a cursory glance, Web Designer is essentially an amalgam of functionality already available in Adobe's Creative Suite (among other software) — the main innovation here is that it's free and more specialized to the areas that interest Google. Somehow we have survived the last two decades with that software in existence, so I am not terribly concerned.

Nope not the end, but the introduction of a tool that real designers can use to do mash ups quicker.