I don't think email is going away. In fact, I expect quite the opposite: Email will expand as a platform for other not-exactly-realtime messaging.

For many years now we have had things like meeting invitations, electronic airline boarding passes, and concert tickets sent via email; I think we will see more things like this, and with a greater degree of integration so that for people with suitably "intelligent" user-agents, these messages will be automatically filtered out of the incoming email and processed separately -- much like we used to do with procmail, of course.