Yesterday at the CW Network's official announcements for next season, they released the official opening-credits cast list for Smallville's 7th season. This means,among other things, that those in the list are under contract for at least 13 episodes next year. Being under contract means (again, among other things) that the production company is obligated to pay the castmember the negotiated base salary for that many episodes, and you can rest assured that if the production company is on the hook to pay the actor, they're going to figure out some way to use them in the shows.
Kristin Kreuk, Allison Mack and John Glover are all officially listed as opening-credits stars for next year. For all sorts of legal reasons, the network and production company cannot announce the participation of a openng-credits castmember without a contract in place, and an opening-credits contract means the actor will be in a majority of the episodes. Therefore, their characters cannot be permanently "dead." QED.
(In fairness, we must acknowledge the possibility that something could happen to one of the castmembers between now and the start of S7 production that would change that... but really, the chances of that are miniscule.)
