Citrus trees can drop all their leaves for various reasons, and quite often they will wait until the shock has passed and sprout new leaves. So the first thing to do is nothing - at least for a couple of weeks to see if anything happens. The wood that remains alive will resprout and this will tell you where the branches are still alive. At that time you can prune back all the twigs that do not regrow.
The problem with random pruning on a grafted tree is that you might unbalance the top and bottom growth, and see sprouts emerging from below the graft line which we can see at the bottom of the tree where it changes from green bark to the darker grey/brown. If you see any sprouts appearing here remove them immediately.
The section above the graft looks ok, so it should at least start some growth from above the graft. As soon as you see that you will know how much of the tree needs to be pruned away.
If you are confident that the location is well drained and you think the tree belongs there, then there is no need to pot it. Just water moderately when there is no rain and keep up small feeds as the tree grows.
