These prospects are not just junior players, one is among the top defensmen in the CHL and almost certain to play a large role for Team Canada and the other could be the best defensmen on team USA at the age of 18. If Larsson can get us a top line player for the next 8 years then yes I would trade him.
Like Tri said, I don't think others value Larsson quite as highly as we do. I think he's pretty much guaranteed to be a top pairing guy, but he hasn't shown AS MUCH as guys like Brodin and Hamilton.
Larsson, Gelinas and Merrill are all going to be at least decent NHLers.
Severson is about as close to a slam dunk as there is
Santini is having a fantastic start
Scarlett and Helgeson are playing very well in Albany.
Devils certainly have an embarrassment of riches on defense, but I think it'd be a mistake to give up on one of the three guys in the NHL ATM. I love Severson and he could certainly end up the best of the bunch, but I would move him before Larsson, Gelinas and Merrill. I wish we could keep them all, but there is no way NJ doesn't do a lateral move for help up front