Atalanta, I can't offer advice about your own tree, but we have a pot grown olice tree out in the garden, which has survived last winter, it has all its leaves and looks well. We don't wrap it up at all in the winter, just leave it out.
If you have new leaves, all is not lost - I would leave it a little longer, then perhaps trim off some of the extremities to see if they are in fact dead, and if they are, then cut it back further.
We have lost several of our exotics altogether last winter - 18 year old oleander bushes etc., all gone completely due to the cold.
All I can suggest regarding your pot is - if it's a shaped pot - that you carefully slice the roots as close to the tree as possible so you can pull the trunk out, then work round the roots by hand, pulling out a clump at a time. This is one of the problems of pots which curve in at the top!