Locking the device and wiping it are two different things. A locked device will still show a message sent to it. A wiped device will not, nor will you be able to track it anymore.
Note too that if the battery runs down, it is gone off the network too, or if it is out of range or a wifi node or a 3g connection, it is off the network as well.
And you've just given anyone finding it a whole day to browse around through all your information. The time to put a passcode lock on it is BEFORE you loose it, not after. Without a passcode on it, whomever finds it can just go into your iCloud account settings, swipe the find my iPad slider to "off" and it is gone for good.
Find my iPad is NOT a security feature - it is a convenience feature, nothing more. The only true security feature on an iOS device is the passcode lock feature.