I will just cut to the chase. You don't need the fingerprint. You need the phone. In 99% of the cases, the imprint will be on the reader. You can just highlight and use the imprint on the sensor to get into the phone.
There a reason that any security firm will never allow you to use fingerprints. It takes at least your whole hand print.
What do you mean by highlight?
In real world use I don't think it'd be so easy to pull a clear fingerprint off the home button seeing how frequently it will be used, and it's easy potential to be smudged. Regardless of that though, there's little point in trying to steal it as the phone can be located and wiped (which means no one can use it until the original account details are entered) before they could apply the hack.