Retaking year 9 after missing chunk of school - sensible/possible?

[Tiggles]

DS is one of the youngest in year 9, bright but not outstandingly so. He had an accident mid December and is still not back in school. The earliest he will be back is mid March but that is subject to the school taking him whilst he still has an external fixator on his broken leg (he will be in it for a year or so) which apparently isn't guaranteed, but even so he will have missed at least 3months of school.
So far he has had no tuition etc since he has been off and whilst I am trying to home ed him I am also working from home. The hospital are trying to arrange him tuition but they have been saying that since December. I'm worried he is slipping further and further behind and will come to his GCSEs next year at a disadvantage.
Would it be sensible, or indeed possible, for him to restart year 9 next year?

[BertrandRussell]

GCSEs are in year 11- so if he can go back for year 10 he'll still have two years befor the exams.

I would talk to the head of year 9- I would expect them to be able to sort out work for him.