I can't see how they would get rid of Chomper. Correct me if I'm wrong, but isn't he the most popular character of the series?
Besides, Chomper's character is vital to the morals in the LBT. Mainly, the character shows that you can be friends with those of a different species, or in this case for people races. Seeing that Chomper is a sharptooth but he is still friends with leaf eaters shows a good lesson that you can't alienate people because of a stereotypical idea about a certain group.
But to get back on topic, I don't see Chomper leaving anytime soon. Is it possible, yes, why I would not know, but I don't see it likely.
I do think adding Ruby was taking it a step too far. There are already so many characters in the LBT universe, and all of them don't even appear that much throughout the TV series, besides the parents. If Ruby appeared in one episode, like certain guest characters, then I could deal with it. However, making her a main character just doesn't appeal to me that much.
Besides, having her in the TV series but not in a sequal then creates controversies as to how many more movies can they make before they reach when Chomper and Ruby arrive at the Great Valley. The show gives the impression that it takes place after any and all remaining movies.
Again, back on topic, Ruby to me is an unneccesary character.
I do agree with the idea that Chomper could have not been made a main character, but still appear frequently throughout the TV series. Then he would be like Newmen from Seinfield. He's not a main character, but still makes an appearance frequently.
To sum up my ideas:
Chomper stay in the show, but not part of the gang.
Ruby not in the gang or show at all
I'm sorry for making a long response, and I hope I don't offend anybody with my opinions.