One of the Bonnies grabs him before he can apply the Even More Fire method of problem-solving.
BONNIE?: “What did Other-Me say about just jumping in? Fire isn’t gonna just work again if it didn’t work last time!”
OMAR: “Look, if it’s burned to ash, then-“
BONNIE?: “- you don’t know what’d happen, and neither would I, but I just keep getting weirder when I regenerate, and so does it. Maybe one of the weird things it’ll be will be immune to fire, and then what’ll you do?”
DANIEL: “Um, guys?”