That question presumes that they've acted and they've harmed the environment. They should restore the land, to the extent that they can, but one thing that has been demonstrated clearly—and I'm not picking on the tar sands—is that they have yet to prove they can restore centuries-old peat bogs to perform the ecosystem services they did previously.
If they've acted in contravention of the law and we look at remedies that would right society for that, there has to be both the fines so they're punished for their behaviour, as well as an obligation to make whatever restorative steps they can.