Brandon Mebane being out is a bigger loss than Lynch imo since he is a big part of the run D. Seattle's D is still coming together. Week 1 vs. Rams they were without Chancellor and their top nickel corner, Marcus Burley, and Earl Thomas was playing his first game after surgery.
The defense actually played well in Green Bay but lost to Aaron Rodgers making plays that nobody else can. Last week, the Bears punted on every one of their possessions. It takes elite QB play to beat this defense, especially in Seattle, and I'm not sure Stafford fits the bill.
If the Seattle O-line continues its improvement and can give Rawls some holes and Russ some time, Seattle covers this easily. Slow start would not surprise me: 10-3 at half 30-13 final.