That's a pretty painful option compared to just handling rough objects. I've rendered touchID almost entirely ineffective just by grip taping a skateboard.

The answer to your question though is that, at least on the phone's side, it would require your passcode to login

Well, that would hurt, and you would have to permanently damage the entire fingerprint-- as only a small section of the scanned print is really needed to make a match.

IANAL: but I would imagine a sour faced judge could call it contempt or maybe destruction of evidence depending on the circumstances?

Mine stops working all the time, especially my right thumb.