Mtg: attacking effect, but the creature dies

Question

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?

Answer 1

The effect ends.

This ability is a static ability (another example would be Warded Battlements), which means that the ability is only "active" as long as the permanent is on the battlefield. Comprehensive rules entry (emphasis mine):

604.1. Static abilities do something all the time rather than being activated or triggered. They are written as statements, and they’re simply true.

604.2. Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 113.6.

Answer done.

However, I want to touch on a similar scenario taking into account triggered abilities (instead of static abilities):

If the ability was a triggered ability (e.g. from Bolt Hound), then the effect would stay.

Triggered abilities are separate from the game objects that created them. In this instance, if the creature is removed when the trigger already went to the stack, it will still resolve normally. The only way to prevent this would be to remove the creature before the trigger condition happens.

As an example, if the condition is "At the beginning of combat on your turn", then the creature would need to be removed in the main phase before combat so the ability never triggers.

The related part of the Comprehensive Rules is (emphasis mine)

113.7a Once activated or triggered, an ability exists on the stack independently of its source. Destruction or removal of the source after that time won’t affect the ability. Note that some abilities cause a source to do something (for example, “Prodigal Pyromancer deals 1 damage to any target”) rather than the ability doing anything directly. In these cases, any activated or triggered ability that references information about the source for use while announcing an activated ability or putting a triggered ability on the stack checks that information when the ability is put onto the stack. Otherwise, it will check that information when it resolves. In both instances, if the source is no longer in the zone it’s expected to be in at that time, its last known information is used. The source can still perform the action even though it no longer exists.