As long as you are growing vines rated for your lowest temps, you don't lose but a few buds now and again. Everybody seems to say they have a special microclimate and push things to the next zone or two. Then when the cold snaps hit, you lose buds, sometimes canes and even sometimes trunks, Rarely will a vine die as the roots are below ground. When things get out of hand is the year following a freeze to the ground. The vine overcompensates and pushes bull canes and is more susceptible to freeze the following year. A few of those in a row can lead to vine death.