After watching Show Me the Mummy (Season 3, Episode 5) it’s obvious how the are going to bring back Nathan Stark. They left it wide open if Ed Quinn ever wants to come back.
Nathan gave Allison a logic diamond as a wedding present. He “imprinted a small part of himself” into the diamond. So they will do something like…
…use the diamond to attrack Nathan’s essence from time and reassemble him. Or…
…use the essence of Nathan that is in the diamond to recreate his DNA and create a Nathan clone.
…or something like that. So as always with SciFi unless you have a dead crispy body to show … the person can always come back. And even if you do have a crispy body (Carson Beckett) you can still come back.
When is dead not dead? When you are on a SciFi show.