Sometimes the carbonation is moved to the headspace, this may make the pressure cause the valve to release pressure, win which case you may have to recarbonate. However, if this has not happened and all the pressure remains in the keg, then it will redistribute back into the liquid once the beer defrosts.
Less of an issue freezing in a keg than it is to freeze in a growler. Now I have to refill that thing and recarbonate the flat beer in a 2 liter bottle just so I don't waste it. Just glad the thing didn't shatter.
Secondary: GF Czech Lager
Waiting to be kegged, Italian Primitivo
Kegged&Ready: GF Orange&Coriander, GF Honey Lager, GF chocolate ale, GF English ale, Island mist (zinfandel), Island mist (cbry malbec).
Bottled: Infected Mead, Dry Hard ciders, Accidental Sorghumwine, various unnamed.