I have read that you can freeze tzatziki, but I wouldn’t recommend it. Freezing may preserve its freshness, but cucumbers usually do not freeze well and will be mushy.  If you think you may need to freeze it, you could make half the batch and then also leave out half of the cucumbers. The yogurt dip by itself should be fine in the freezer, especially full-fat yogurt.  Thaw the yogurt and add cucumbers before serving.