Clean up was really an issue better forgotten and left for their future selves, or else for someone else. Preferably someone else. Aziraphale rather hoped someone would take it off their hands; a janitor, perhaps. Surely custodial staff existed, even in enchanted schools. Especially in enchanted schools.

"Really? Though I would be a little concerned we might cancel each other out," or cause a worse explosion, with his luck, "but then I can't say I have much experience with multi-person spell-casting."