Is there a way that I can find out how a campaign was structured on a specific date? Or maybe I can do a back-up of a campaign? I haven't heard anything about that, so I hope it's possible.
You can look at changes over the last three months, but that's about it, as far as I know. In terms of backing up a campaign, I would imagine that you could probably save a copy of the campaign using Adwords Editor, though I've never had occasion to do it...