Hello, can you list what you have backed up, and what you don't? I would suggest making a backup of everything you have now, so that if anything gets worse, you can always revert back to this state.
One thing that is probably undamaged, unless you deleted it yourself, is the set of partitions modemst1/modemst2. If you still have these backed up, there is hope! For me these were the only partitions that I needed from my actual phone, and not from someone else's.
The QCN file in this thread worked nicely for me in combination with my own backed up modemst1/2 files. And don't forget to flash the kate modem firmware!
If you don't have modemst1/2 files, I have some backups you can try, but there are no guarantees. Ultimately you CAN get your phone working again unless there is hardware damage, it's just a matter of finding the right combination of backups from other phones, sadly there are many many versions of kate phones with slightly different configurations.