You should be being set work to do at home- if you are not, I would get your parents to speak to the school after Easter. I think lots of schools are putting better plans into place for after Easter. This will have to be more self directed than usual, but you should be able to get teacher support via email, and learning to work in a self directed way will help in the long run.
Everyone is in the same boat, so grade boundaries next year will reflect this.
If schools don't go back in September, then I would expect some consideration for your year group- e.g. the format of exams may be changed slightly. However, if we go with Arlene Foster's 16 weeks, then we could see schools going back for a few weeks before the summer holidays.
I know this is tough, but try not to panic- if your year group are severely affected then I am sure a plan will be put in place.