Jon is correct about your likely losing data if you restore from Time Machine, so if that's an issue you'll have to travel another route.
This would obviously apply to
any personal files predated by the Time Machine backup in question, not just emails.
However, restoring from an earlier state via Time Machine shouldn't erase anything on the Time Machine volume, so all those later files will still be available there, backed up during subsequent Time Machine runs. (This assumes alan has continued to backup via Time Machine since the installation of Safari 6.0.2.)
