I can't fix the problem, but I can get your party members back. I just posted the beta of K1 toolbox here
. In it there is a tool for managing your party. Install the toolbox beta by running the EXE. Then add the item jc_party
to your inventory with the cheat console or KSE whatever. An Address Book item will appear in your inventory and you will be able to activate it in the GUI where all the armbands appear. Do that and it will trigger a computer console, and you should be able to figure out how to add the missing party members from there.
However, whatever equipment they had on them when they went missing is probably gone forever, and you'll have to level them up again. Assuming you have been saving often and in multiple slots, you could go back and check what you lost so you can cheat that back in. I can't comment on whether the progress of their personal side quests will be affected.