Sorry, the meeting was earlier this week, I should have updated before now.
The school were actually very supportive.
They have officially ended the exclusion, however they have granted him study leave for the duration of the prelims. They gave him a study pack with revision material and the classwork that he will miss.
They've made a referral to a local youth substance abuse team where he will meet with a councilor, what the next step for that is depends on how the initial chat with the councillor goes.
They appreciated his letter of apology, but were clear that the letter alone was not enough, and they asked both of us to sign a behaviour contract.
He will also meet with the Ed. Psych to have a review of his support needs (he was diagnosed with Aspergers and Sensory Processing Disorder as a young child, but its mild so hasn't received any support with this for years).
There was no further talk of permanent exclusion, however they were very clear that a repeat of this would not be tolerated.
All in all, it was a lot better than I had been fearing.