Hi Hamish Harvey
No, for now you cannot just delete them from projects ( images or scans ) but you can disable them and export them as a COMPONENT with only the data you want to preserve.
From my experience: I NEVER delete data about that I am not sure they could be later used for whatever reason = proper planning ( proper backup strategy !! )
How to open the problematic dataset ? you can create files with the missing data, for images you need to create the same resolution image, even plain filled with any color so that RC can open it. For the scans you need to create a workaround, the easiest way is to rename the other (same resolution ) scans and rename them to the missing ones. To get better workflow on this, look in the RCPROJ file, where are stored the plain-text paths + filenames…