Hi @Ben_Cohan,
In most cases, content is going to be associated with a course shell, not a specific user. There is a chance some that external app integrations (including item banks in New Quizzes) might be affected, also if the designers put files in their user folder instead of the course folder that could be an issue. I'd say the easiest way to check this would be to delete the users accounts in your test or beta Canvas instance, then check courses in whichever instance you use to make sure things are functional. I'm not sure how many courses they were involved in creating, but they more than likely used similar methods in every course, so spot checking a few courses should give you a good idea if anything will actually break.
Hope this helps a bit!
-Chris