Quoting: jake4leafs
if a deal is in place, campbell agrees to sign, giving up blackwood for him isnt a problem,
you're banking on an enormous "if" right there - and you're also just breezing over the fact that Campbell is signing for a least a $5M AAV while Blackwood makes $2.8M this year and Vanecek probably re-signs around $2M - so both the goalies currently in Jersey probably cost about the same as Campbell on his own, despite the fact that Campbell's track record isn't that much better than the 2 guys already in Newark *and* he's several years older than both of them:
Campbell: 30 years old, .916 SV% / 2.53 GAA in 135 career GP
Vaneeck: 26 years old, .908 SV% / 2.68 GAA in 79 career GP
Blackwood: 25 years old, .907 SV % / 2.94 GAA in 130 career GP
Put it this way: you're Tom Fitzgerald, Devils GM, and you're trying to build the best team possible. Which makes more sense to you:
Scenario A: You have 2 goalies in house, but you like Jack Campbell. After noon on July 13, you start negotiating, and maybe he signs, maybe he doesn't. If he signs, you look at Mackenzie Blackwood and move him for a mid-round pick to a team looking to upgrade their goalie tandem.
Scenario B: You have Vanecek & Blackwood in house a day and a half before free agency. You like Jack Campbell, and you trade Mackenzie Blackwood for the right to have an extra 36 hours to negotiate with Jack Campbell with no guarantee that he doesn't actually test free agency - after all, he's made it this far, what's another 36 hours to wait and be able to negotiate with the 31 other teams?