Why do you need to delete the whole drive? If the current OS is working without problems, just leave it installed. It's probably not the one that came installed on the machine, anyway. You can certainly erase any apps and their data that you don't want to remain on the drive. Mostly I'd just delete any financial stuff and probably emails, contacts, and passwords. You can also delete that stuff that might be on an internal Time Machine drive. Don't make things harder than it needs to be.
One other thing you might want to do is delete email accounts (and email) and reauthorize the computer in iTunes.
Thanks, I may try that.