My lifetime mpg on a '94 MT Civic was 39 - 40, so I'd say you have a good chance to stay in the high 30's FE, but maybe not much more, because the civic has grown a lot in size and weight in the last decade.

R2-E2, 2G Prius.
Highway/City/Husband/Wife MPG: 56.5, as of 12/2005, 26K miles

Jac Nasser, Ford President: "We are planning to launch a hybrid version of
this car [P2000] within this year [1998]. We will also make FCEV available in
2004."