trunk splitting is also an issue up here w things like ornamental cherry trees and some young maples because the sun warms up the sun facing trunk while the back side is shaded and frozen...if you are concerned about this you could place one of the grow tubes around the truck to get it thru your winter....the shade will even out the temp on the north side of the trunk
what you are speaking about is the main reason that many of my vines have multiple trunks
while trunks can heal there are no good things that can come of it long term, among them grown gall, where soil borne bacteria enters the wound via things like splash from rain.....when you see this you have to prune at least six inches below the wound and that may not be possible w a grafted vine....vines on own rootstock will be ok once a shoot comes up from the ground
also, sap does bleed from the vine....when pruning is done early enough it is minimal...done later in the year you will see a mess of it....looks nice when its flowing....but when it gums up its an ugly thing to see