Don't forget, he's also playing under 15 minutes a game and would probably have close to 40 points if he played close to 82 games.
In Seattle, he'd be a top 6 guy getting 17+ mins a game, so he probably could get 50 points.
I do think Tampa will attach a pick with Johnson for Seattle to take him though, simply because they'd have to leave someone good exposed.
But he'd be hard from a bad pick. A former all star, Stanley cup champ, born and raised in Spokane, now playing for Seattle? Would be an easy sell for the franchise, and he'd definitely have a good shot of being the guy who sells lots of jerseys.