It is possible to rejuvenate a half-dead 6 ft tall cedar tree?
If not rejuvenable, could we grow a pretty vine on it, but one that is non-invasive?
If the tree is only half-dead, and you can determine the cause of death, and take steps to stop the dying, then the tree might live to a ripe old age. So what happened to the tree -- was it injured by lightning, or a lawn mower, etc? If not damage, look at the tree trunk -- are there slimy or weeping or peeling spots? Then look at the leaves -- are they brown, yellow, white? Are there spots? What do the spots look like, and where are they? Are there bugs on the branches, or on the leaves? These are just a few of the things to look for. If you want to save the tree, you should probably enlist the help of a professional, an arborist, or someone in the Master Gardener program which you can access through the nearest botanical garden. In addition, here are a couple of articles that might help you: https://www.gardeningknowhow.com/ornamental/trees/cedar/growing-cedar-trees.htm
As for growing a vine, there are many you can choose from. Many of these would work for you -- make sure any vine you choose is hardy in your area: https://www.gardeningknowhow.com/ornamental/vines/ovgen/growing-plant-cover-fence.htm