While 99% of the time this doesn’t matter if you roll several dice or just the 1 dice for all the darts, a player did something which seems contradictory and knowing the true answer to this would clear up a lot of uncertainty.
They cast magic missile after using Hexblade’s curse, to add their prof to each damage roll. Then after used the Empowered Metamagic to reroll the 1 for all the darts, into a 4, and topped it all of with the wizards Empowered Evocation to add their INT to the dart.
The way I see this the Hexblades curse would only work several times if you were treating each of the darts individually, by rolling them out separately. This would have the benefit that the Lore Bards cutting words can’t cut the damage down to zero as effortlessly, by cutting the 1 dart that is multiplied down to 0.
But if treated as an AOE the Empower Metamagic and wizards Empowered Evocation would work. This also matters immensely when considering how magic missile works on damage thresholds (others have answered, and it seems to contradict again).
So my question which way does it work?