Do you have a save before the elementals disappeared, or before destroying the staff, that you can revert back to?
You could use the
Save Game Editor to give yourself the 'Ice Shard', but without the quest update from talking to Sua, I don't know if it will work to summon him in the prison.
You can continue without freeing the White Witch, though will miss experience and some of the story that way.
You can email supportdos@larian.com, with a description of the problem and the report.zip file generated by the
D:OS Analysis Tool (for the PC version). The report will contain system and game information, as well as your saved games. To reduce the file size, most of the saves can be deleted; leave your latest, and maybe one before destroying the staff.
For Mac, saves can be zipped by right clicking the folder(s) and selecting Compress, in the folder:
~/Documents/Larian Studios/Divinity Original Sin/PlayerProfiles/<ProfileName>/Savegames
