A factory reset will not cause the phone to brick, it will simply
restore the phone to its default configuration (and remove all you
husband’s personal settings and downloaded software). The phone will
still be S-Off and rooted even after a factory reset. If for some reason
the phone needs to be returned to Verizon he’ll need to go through the
unrooting process.

You really have to work pretty hard to brick the phone… or do
something like pull the battery during an HBOOT update.