The advertising networks being the last to use it is something that will make Flash's implosion very quick and sudden, IMO.

If uninstalling flash only causes you to miss out on ads, it makes uninstalling flash that much more attractive. Which makes the advertisers want to get off flash that much sooner.

It needs probably just one or two more use cases to disappear (Facebook video is one of them), and its final death will be quite quick.