Jonah should have stayed

I've just got back into the series watching all the old 80s episodes on YouTube and I think it's a crying shame that Jonah Jones left after only two series, I know there's been rumours that either Lee Sparke misbehaved and was sacked by having Jeremy's drowning storyline originally written for him and that the events leading up to it were either because of Jonah being discovered as being a class genius or his pranks getting to irritating highs for the rest of the class, but I've never been able to find a concrete answer, surely the then producer Ronald Smedley could have brought him back in time for Series 9, I think he would have been ideal for the Zammo drugs storyline as he witnessed his old friend hitting rock bottom and tried to help him kick his habit, oh yeah and he DEFINITELY should have been in the sixth form!