Does afflict trigger if the attacking creature is blocked but the blocker dies before damage?

Afflict triggers the moment the creature becomes blocked, which happens during the declare blockers step (CR 509.2). At that point, the game registers the creature as blocked and any 'becomes blocked' abilities — including afflict — trigger immediately.

Afflict reads: 'Whenever this creature becomes blocked, defending player loses N life.' The keyword is defined in CR 702.130. Crucially, the trigger condition is becoming blocked, not dealing combat damage. These are entirely separate events.

Once a creature is declared as a blocker in the declare blockers step, the attacking creature is blocked for the rest of combat — even if the blocker is subsequently removed (CR 509.1h). Whether the blocker dies to a spell, an ability, or combat damage before the damage step, the attacking creature remains blocked and afflict's trigger has already occurred.

Example: You attack with a Torment of Venom creature with Afflict 3. Your opponent blocks with a 1/1. In response to the afflict trigger, your opponent casts a pump spell to save their creature — but afflict has already triggered and resolves, so the defending player still loses 3 life regardless of what happens to the blocker.

The only way to avoid afflict is to never block the creature in the first place, or to prevent it from 'becoming blocked' entirely (e.g., via an effect that removes blockers before the trigger resolves — but note the trigger has already been placed on the stack).