Obviously you can always get back into education. My PGCE was with the OU, after a gap of 15 years from 'formal education' and my brother has his first degree with the,
The best students that I ever worked with at university were mature students. But it is so very much harder to do it that way.
Many people will 'only' need the paper qualification to get onto a course that they want, or to get a job that they are interested in. the reality is that many employers do want to see the paper qualification.
You can say that a holiday will be educational, but for most of my students it simply involved lying on the beach. and you are about to type that family life is a vital part of a child's education ( (I've done this discussion a few times before ) and I would agree with you. But for the vast majority of the kids I teach they are not going on a trip to the ;local caravan site, as this is the only time the family can afford, it is going to Goa rather than Spain. the educational input of most of these holidays is near zero, and will have negligible benefit to their GCSE results.
If their parents don't think the GCSEs are worth it, that is their right, it is their child, but they cannot pretend that there will be no impact, because there is.
Apart from a few cases, most children will not be adversly affected by missing out an a specific holiday. they are likely to be adversly affected by missing this particular time in the schooling.
I was once asked to give up my lunch to tutor an A level student who was going to miss my lesson. When I asked him the reason, he told me that he was going to see a gig. I told him the page numbers that he would be missing!