When I have a card, that gives attacking creatures +1/+0 and I attack, than a spell kills the creature that gave the effect, after I already declared my attackers, is the effect still on other attacking creatures ? Or is it gone?

Neck Breaker (the transformed side of Breakneck Rider) gives attacking creatures +1/+0. If I attack and then a spell kills the Neck Breaker after I declared my attackers, does the effect remain on the other attacking creatures?