Nothing much happens when the CAT goes, at least I did some over 10 000 miles with broken or semi-broken CAT on my bike, you'll lose a bit top end power that's hardly noticable (probably because of slightly higher back-pressure from a little clogged exhaust?). But prefer non catalithic-converted exhaust riding in most of third world since you're forced to run on leaded fuel quite often. I'm sure you can make or modify a connecting piece that lowers the current aftermarket exhaust you have. Also on 1100/1150s you can cut out the CAT from the exhaust. CAT element is basically a cone-shaped little piece inside the bottom square exhaust on BMW 850/1100/1150s, placed exacly where the header pipes got into the exhaust box - all you have to do is cut out a piece of metal off the surface on this area to get the access into the exhaust box, grind off the CAT cone and weld the hole closed again on the box'es surface - and you'll have the same exhaust without the CAT. Mate of mine did it as well, but his CAT element got loose itself (lot of bad roads+vibrations!), so he had to remove it because of the noises coming from the bottom exhaust and CAT didn't work anyway being broken off itself
Search web for pictures how to "cut the cat" - I've found some previously since I was planning to do the same thing till I bought an aftermarket exhaust.