I've done that : copy my saves using iphone explorer, and then uninstall avadon, and then delete from itunes, redownload, reset of ipad, reinstall, recopy the saves and lauchn the game and I still can't talk to NPC.
I think this is the save wich is corrupted, not the application.
I occured this time sometime between the beginning of the rat cave and returning to the NPC who gave me the quest.
During the rat cave battles, I noticed at least one crash of avadon (it happens before, only during battles). Restarting the game was ok, it restarted almost at the time of the crash. Perhaps it's linked to the 'talk to NPC' problem.