Seattle winning is bad, but a Lions win wouldn't be the end of the world. Right now, Dallas' tiebreaker over Seattle is null because of the three way 9-4 tie. If the Lions win, they'll be 10-4 and Seattle would be 9-5 with a loss. That means Dallas jumps to the 6 seed ahead of the Seahawks.
But it looks like the 49ers are crapping the game away.