So today I was going to pause some ad groups in a Micrsoft(Bing) campaign & then enable other ad groups. It's something I do often testing different URLs with identical keywords in the groups. Typically to save time, I select all of the 51 ad groups in this campaign to pause them even though most already are. I obviously wasn't paying close attention because I deleted all the ad groups instead of pausing. Yep - I even hit that verify button without looking close to see I was about to delete them. I've been building these keywords for months (many thousands) & I didn't have the up-to-date keywords saved on my computer (another blunder!!!).
So I go to the "Change History" tab in my account to see that I couldn't undo these changes of ad group deletion unlike other changes that you can undo. Panic set in while I waited to get a rep via chat to hopefully correct my mistake. Well the rep couldn't get it done through some methods but is going try another way but it doesn't sound promising. I will find out if it is successful in about 24 hours. (update - no luck undoing my mistake)
So... learn from my mistake & don't do what I did. Pay attention to what you are clicking & keep up-to-date keyword files from your campaigns/ad groups on your computer.