Hi!
For me at my university, if you go in voluntary you can suspend your studies (if for a long time admitted) and return when you need. If sectioned, you need to be cleared by your psychiatrist to be ok to return to uni
Yes, you should have arrangements for mental health admitted or not, such as extra time on exams and extensions on coursework if needs be.
You can also apply for DSA which can cover a mental health mentor who can help with all the above