@GAGLine is bang on. The NHLPA should not and would not agree to end guaranteed contracts.
Guaranteed contracts protect marginal players even more than the vets. The vast majority of NHL players don't play as much as four full seasons. Those that do make it through are both very good (the best of the best) and lucky (to avoid injury and have the opportunity to play).
Signing a prospect to a massive non-guaranteed contract means nothing if the player is never able to establish himself in the NHL. At least with guaranteed contracts, those that do hang on for a few years make good money while they are there.
Otherwise, it's a race to the bottom in a very perilous profession,