cant I am finding it hard to believe that half the school are 'vulnerable' in what context are you describing vulnerable?
A school could easily open with 50% staff, as obviously lots of children will also be off ill/classed as vulnerable. School could offer a reduced timetable, larger class sizes in the short term, and packed lunches only for instance. Of course it could be done.
Teachers and children will benefit from the return to normality, families can go back to work and we can monitor the situation.
It may not suit you for schools to open, but without the scientific facts to support the decision to close them i.e. children at serious risk, then I would expect all schools to reopen after the peak (which will be around Easter)
The country and economy will need to be restated as soon as possible, or the consequences of this virus may be far reaching and more damaging than coronavirus itself.
If it turns out that children are in danger from cv, and they are at serious risk then of course the schools should remain closed, but this would have to be backed up with data and statistics, so far this has not been the case anywhere in the world, and I would not expect the UK to be any different.