Hi @BradThames 

It depends on exactly how you "unenroll" them.  

If you sent their enrollment status to "Inactive", or if you "Conclude" their enrollment, they will no longer have access to the course, but you will still be able to access their assignment submissions (by going to People > [user] > Grades).  However, if you "Delete" or "Remove from course", the submissions will be gone and you will not hav access to them.

Likewise, if you completely remove the user from the system, their submissions will be gone.