Whilst when you are doing them, GCSEs are hyped up as the most important thing in your life, they really are not.
You need enough to gain admission to your chosen post-16 course.
You need maths and English, and occasionally something else (eg a science for primary teaching).
Universities may look at the grades, but will also look at information provided about extenuating circumstances.
Most sixth forms will use their discretion in the case of a child who has had a bereavement or other trauma, and because this will be at a local level, can talk to the school (if not staying at the same one) about suitability for the course.
There are autumn resits for maths and English.
Nothing's ideal, but it's very difficult to set a fair tariff for how much extra to give; some kids might be unable to think at all, whereas others may be able to switch focus and perform much as normal.
Some kids might be prouder of "6 despite circumstances", than "8 but probably only because they gave me extra because of..."