Title says it all, right? :-)
If you put your nation on vacation mode, it'll be fine for 60 days and it will cease to exist; if you don't, 28 days is when your nation will cease to exist. If you want to keep your nation alive, I'd suggest having someone you trust 100% log into it occasionally to keep it alive, while it's on vacation mode.
If it dies, you can resurrect it easily enough with a Getting Help request. You don't even need to log in. That's probably safer than giving it to a friend.