Subarus, like Toyotas, are very sensitive to overfilling of the gas tank. Hopefully this one incident will not destroy the carbon canister that is the heart of your evaporative emissions system, but I suppose that it is possible for one incident to do it in.
If it is never again overfilled (or topped off), hopefully you can avoid the expense of replacing that carbon canister. The last time that I checked, replacement of that part cost somewhere north of $400.00, so you might want to tell your husband to start putting money aside for this repair in case it is needed.