Spoiler: SOD
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I believe that was actually the treants - they were trying to avoid a fire he started but he didn't actually destroy the gate himself.
It would be like if someone lights your house on fire and you break down your door to escape - they might be responsible but you still broke your door, except in this case your door is one of the corner stones protecting reality, frankly Lirian was likely being a bit of a jerk when she superglued (or whatever) the treants to the gate.