Rob if and when you de-cat, get it done so that you can put the cat back in when needed.
My exhaust is done such that I have replace the whole system not just the cat if it needs doing, I used to do this when it failed MoT on emmission, but now I just risk it.
Never noticed any real difference if I'm honest but does sound better without.
Good luck with the bodyshop, I'm getting some quotes in next week.