Well it's not automatic 2 year prison sentence. The state charges you with a crime, it goes to trial, and then you have to defend yourself - if your argument is that you forgot, then it would be an interesting case - ultimately the prosecutor would need to prove that it's unlikely you forgot, say if they had proof (say CCTV recording at the airport) showing you using your phone 5 minutes before it was confiscated - it would be pretty hard to argue that in the space of those 5 minutes you forgot the password. But if you had a device in your suitcase and could successfully argue that you haven't used it in ages and the password was long and complex then yeah, I guess you'd be found not guilty - up to the judge/magister/jury depending on where exactly in the justice system you end up. But yeah, while stopped at the border saying "I forgot" is not a good card to play.

It probably won't end well but I'm curious what would happen if you give them a password that resets the device. Theoretically it unlocks it, it's just that it takes a minute and it's factory new at that point.

They'd charge you with destroying evidence, or "perverting the course of justice". They aren't stupid, they would know that you gave them a password that wiped the device.

They would image the device and try the password against the image, if possible.