At very low pressures water is only stable as a gas or solid. Initially water will boil off rapidly, causing the temperature to drop, and eventually causing parts to freeze. If the ice is able to block the breach (breach is small compared to volume, and an ice dam is able to form), then the water boiling will cause the pressure to rise until liquid water is again stable, or the ice dam blows out and we're back at the start.

You should be able to get a fairly wide range of equilibrium states depending on initial conditions.