Does Spell Queller exile the spell even if Spell Queller leaves the battlefield before the trigger resolves?

Spell Queller has a triggered ability that triggers when it enters the battlefield: 'When Spell Queller enters the battlefield, exile target spell with converted mana cost 4 or less.' This is a separate trigger that goes on the stack after Spell Queller enters. If an opponent uses a removal spell in response to kill Spell Queller before this trigger resolves, the trigger does not get countered automatically — Spell Queller's location when the trigger resolves does not inherently matter for the exile effect itself, since the ability has already triggered and is on the stack.

However, the key nuance is timing. When Spell Queller enters the battlefield, both the 'exile' trigger and any removal spell stack up. If the removal kills Spell Queller BEFORE the enter-the-battlefield trigger is even put on the stack (which is impossible under normal rules — triggers are placed on the stack at the next available opportunity after the triggering event), or if the exile trigger has already resolved, the exile happens regardless. Under CR 603.6, a triggered ability still resolves even if its source has left the battlefield, UNLESS the ability specifically checks for the source's presence.

In practice: Spell Queller enters → exile trigger goes on the stack → opponent casts removal targeting Spell Queller in response → removal resolves, Spell Queller dies → exile trigger STILL resolves because the source leaving doesn't invalidate the trigger (CR 603.6a). The spell IS exiled. BUT — if the spell is exiled, when Spell Queller leaves the battlefield later, its 'leave' trigger will return the exiled card to its owner's hand.

So the real danger is a different sequence: if an opponent can respond to Spell Queller's ETB trigger by destroying Spell Queller AND the ETB trigger somehow fails to resolve — but under the rules, the ETB trigger resolves normally even with Spell Queller gone. The verdict is: Yes, the spell is still exiled even if Spell Queller leaves before the trigger resolves, because CR 603.6a allows triggers to resolve after their source leaves the battlefield.

Example: You cast Spell Queller targeting your opponent's Lightning Bolt. The exile trigger goes on the stack. Opponent responds with Shock to kill Spell Queller. Spell Queller dies, but the exile trigger is still on the stack. It resolves: Lightning Bolt is exiled. Then Spell Queller's 'leave the battlefield' trigger also resolves, returning Lightning Bolt to the opponent's hand.