As per a discussion I had with a member years ago. There won’t be any problems opening the projects.
But for example if you guys use a plugin/feature in the Pro version that is not available in the artist version.
It will not show in the artist version.
Like AP says it will open fine in Artist but the Pro features will not be available. But this doesn’t mean that feature/setting/whatever gets removed from the project - it just can’t be used. But when the Project is next opened in Pro the Pro stuff will still be there & working. FYI this is also what happens when opening a Project in an earlier version of Cubase.