When the door is unsealed- so is time. Stones fall from where they'd been caught, demons crackle to life, Tevinter mages recoil in horror while attempting to defend their lives. In the main hall the frozen rift spits and crackles with life- pouring out yet more demons unless sealed. If left to their own devices the Tevinter mages will fall back from the antechamber in an attempt to collect their bearings. IN the scuffle a journal is dropped, open to it's final entry:

Helladius ignores all results that do not support his own hypotheses, brushing them off as "anomalies" and "expected deviations." He posits that there will be an acceleration in the channel's creation—and will no doubt test the theory without guaranteeing a secure channel can even be maintained.

I have argued the inherent risks, the catastrophic tear in the Veil that will result from such foolishness, but he has the others convinced. He grants only a sneering permission to conduct countermeasures in the event of failure.

If I am correct, the only course of action will be to redirect the resulting power into sealing the event itself. The odds of survival are less than ideal, but the surrounding lands will be preserved.