Any question answered...

In existence (both exist)

Mass:
Matter + anti-matter = 0
Energy:
Matter + anti-matter = 2mc^2

Out of existence (both do not exist)

Mass:
No matter + no anti-matter = 0
Energy:
No matter + no anti-matter = 0mc^2

Zero before, zero after, no change in amount, conservation conserved.

(Please remember, I don't know what I am talking about)

Isn't that (^^) actually the case? Where does this energy come from?

EDIT: Emyr beat me to it.