Catalpa are far better pruned in winter when they are dormant so your neighbour did not do you any favours. I suspect this part of the tree will NOT come back although new growth from the main stem which pushes out in that direction may well replace it.
I would definitely prune off all the dead wood on that side at the end of the season to make sure no fungal diseases or anything else are going to spread into the main tree.

Thanks Bertie, I had a feeling this would be the answer, my poor tree looks really lopsided, it has lovely lime green leaves our side and nothing the other side, it has really spoiled the look of it, I am so angry that my neighbour didn't talk to me first, we will just have to see what happens next year.
Thanks again.

I know it's no consolation but at least you have the lovely side and they have to look at the pruned side. They could have done you the courtesy of asking you first.

Yes there is that I suppose Cammomile, I only hope the rest of the tree hasn't suffered in some way, fingers crossed, if it has then I will just plant another one further in the garden, fortunately we have a large garden.

I doubt that the whole tree will be damaged by this, but my experience with Catalpa and Paulownia too (which has similar looking leaves and growth habit) is that they don't like being hacked about when in growth and this can cause die back. They always seem to come back though with new shoots coming from the main trunk or lower down so I would think you will be ok.
Keeping my fingers crossed for you!

Thanks for that Bertie, I hope you are right, this tree has been my pride and joy for many years, I have enjoyed sitting under it in hot weather (not much of that this year!) but if we suddenly had a hot spell now I'd be out of luck, again fingers crossed we see some new leaves on the main trunk next year.

I have posted a couple of photos for you to see on my photos page.