Even lots of people that are not directly active in the email space owe a part of their income to them, I find it a lot easier to imagine a world without smartphones or the web than I find it to imagine a world without email.
I wonder how much the economy would break down, and have to change, if email suddenly went away?
And even if someone doesn't use it that much for personal communication, it's part of the underlying net infrastructure (think account-creation verification emails, password reset emails, bank statements, etc).
Or suddenly went proprietary.
It might even happen.