Deaton, Scott and others in “Unfinished Business”

Essentially, you, Allison, and Stiles need to be surrogate sacrifices for your parents.

Scott

We die for them?

Stiles

But, he can bring us back. [to Deaton] You can... you can bring us back, right?

You remember the part where I said it was dangerous? If it goes right, the three of you will be dead for a few seconds. But, there's something else you need to think about. This is a dangerous thing for more reasons than one. You'll be giving power back to the Nemeton, a place that hasn't had power for a long time. This kind of power is like a magnet-- it attracts the supernatural, the kind of things that a family like the Argents can fill the pages with a bestiary with. It will draw them here, like a beacon. [...] It'll also have an effect on the three of you. You won't be able to see it, but you'll feel it. Every day, for the rest of your lives. It'll be a kind of darkness around your heart. And permanent, like a scar.