Kamelion probably sounded like a good idea at the time, but wasn't.
The reason why the Kamelion robot was used fully only in two serials was that it was very difficult for the Doctor Who production team to control. It malfunctioned frequently, and things were only made worse when its inventor, Mike Power, died in a boating accident without leaving behind the knowledge of the complex codes that controlled it.
A third appearance by the character in the serial The Awakening, designed to bridge the gap between its appearances and to remind viewers of its existence and the fact that it had been 'hiding' all this time somewhere in the TARDIS, was cut for timing reasons and was never broadcast.
Kek, he was doomed.
Onscreen departure Edit
There was no such problem off TV, so one of the novels had him survive so they could use him again. He proved so popular that he made cameo appearances in three more novels and one audio and died again. Maybe it's not entirely his fault, as anyone who wants a past-Doctor story with Five wants Nyssa or Peri, not Tegan and Turlough. Even his audio is a Peri story with Nyssa returning inside his brain.
But there is that Short Trips story where he fucks the TARDIS. She gives birth to a human who looks like Peri, but can grow up as fast as she wants like Melody Pond, so she grows to boobs age in a few days and then stops there. They drop her off to take Peri's place on Earth, and nobody notices any difference because there's only two things anyone ever notices about Peri. Why wasn't that on TV?