sync with Google Classroom

If i have already set up my class on khan prior to using google classroom, if I now click on the sync with google classroom option on my class settings in khan will my students accounts stay the same or will it create new accounts based on their emails in google classroom? I just want to integrate the accounts that the students have currently been using -  with our google classroom since that is what my school is now using. I do not want to create new accounts for them and confuse them. The accounts they are currently using were manually created by teachers using a teacher created username,password and class code and not linked to our school gsuite or gmail. The teachers log in to the teacher dashboard through the school gsuite but that is about it. Please help. Thank you.