Ask Kef if they will replace the uni-q. Or if out of warranty sell you one. The way these things are constructed, if the tweeter is gone, it will be very hard to replace just that part. When folks have blown their uni-q drivers on the q series or LS50, I’ve seen them get replacements of the whole unit directly from Kef by supplying a serial number of the speaker in question. One used to be able to just buy the drivers for diy but Kef put a stop to that about 8 years ago.
At for how to get it off, I am guessing it is front mounted and the trim ring is glued over the flange. Kef should be able to verify this.
Also, one should be able to test the crossover electronically with a meter to rule that out. Good luck.