From my personal experience my school did everything they could to actually KEEP me in school and get me through my exams. I ended up repeating a year of a levels so didn't have the support of CAMHS in year 13 but my school was amazing!
In year 12 MY in school attendance was 47%, when I repeated the year my in class attendance was 39% and yet they still kept me and didn't threaten to kick me out at all. When I told them I wanted to drop out in year 13 they said they wouldn't let me because they knew how much doing well meant to me etc etc!
So, I highly doubt they will kick you out - after all, they want their students to do well and be healthy so they should pull out all the stops to try and help and support you as much as possible!