They should have a fine and be required to fully restore the land they destroyed.
We don’t let someone who stole a tv keep the tv, not should we when they’re stealing public resources.
Otherwise the message is very simple: breaking the law only adds to the construction cost but let’s you keep the construction.
No, they shouldn't simply be fined and required to restore the land.
In addition to all of this -- they should be put in jail.
That's the only way these people will begin to get the message.
But in the US especially it seems unlikely law makers will ever hold the people who pay them culpable
An eye for an eye doesn't work when one person values their eyes less. The perpetrator must see punishment greater than that experienced by the victim.
That being said, where I live the people involved would have likely risked real jail time.