How bad is it to have wet insulation?
If your insulation is damp, chances are good it could freeze or stay damp for a while.  If not too much is involved, it would be a good idea to remove it to a warm place to dry out, or simply replace it.  Never a good idea to leave wet material against ceiling drywall.  It could dampen and ruin the drywall. If left too long, mold or mildew could result.  The snow coming through the vents is probably an isolated event.  Don't close the vent.  Maybe just lay a sheet of 4 mil plastic over the insulation to keep snow off your insulation.  Keep an eye on it.  If it happens often, consider a better louvered/screened vent fixture that won't allow snow to blow in as easily.