I admit, poor Chomper does seem to have a problem being in the Great Valley itself. Even if he could hold off eating Leaf Eaters if he were to stay away from them, being in the Great Valley for him trying not to crack, especially if he gets hungry and temptation comes knocking at night, to whack someone, it would be like someone trying to stay off chocolate while craving it and deciding to live in Willy Wonka's Chocolate Factory for the rest of their life. They'd go nuts if they didn't cave. It can't last forever unless a substitute is found.
As for Grandma and Grandpa Longneck, we don't know how old they are nor how long their kinds live. They could be around a while.
I think a really creative solution can work to the Chomper problem, but, barring that, he's gonna have to go, yes. I just hope LBT can think of that really creative solution just like the Star Wars the Clone Wars people were able to do with Ahsoka Tano, which, by the way, before the episode "The Wrong Jedi" aired, was as equally unsolvable as the Chomper problem so I'm even more strongly resolved not to give up hope, which it seems you have.
Believe me, I've argued against the odds in a major cartoon, with forum members and even the staff opposing my position and saying how impossible it was, and won before. Don't doubt me.
There are ways to solve both the Chomper and Grandma and Grandpa Longneck dying too soon problems. You just need to get REALLY creative. Having either, or, heaven forbid, both the negative events you list as "practically inevitable" would be fatal to the series, or at least a bigger blow than the tragedy of the death of Mama Longneck. On the other hand, a clever plotline, yes taking some leeway and perhaps altering some stuff a bit, could work.
I mean, in the Star Wars the Clone Wars, they were to bring back Darth Maul and save Ahsoka, even though she shoulda been screwed as Anakin's Padawan and not being in the third movie, and Maul was supposed to be dead.
Yet, their stories sound believable enough that I can accept that Maul could have survived, half mad, with his lower half missing, and that Ahsoka could be expelled, reinstated but refuse to rejoin, feeling betrayed, hence she would not have been on the list of the Lost (Jedi who left the Order), the expelled (as she got put back in), wouldn't be in Episode III, and would survive Order 66. And Anakin would be pissed about it and move closer to the Dark Side all the same and hence her death wasn't needed to further the plot line, as so many had argued against me that it was.
Clever solutions and plotlines. Happy audience. You need to learn to think outside the box.
Anyway, I think chomperrules1993 and The Lone Dragon might back me. Especially chomperrules1993. I'm not alone.
Also, I've seen fanfics where Grandma and Grandpa ARE alive when Littlefoot and Ali have kids, so clearly everyone doesn't think they have to die either.
However, I think we've said enough on this topic. Given the kid friendly nature of LBT, I think, should they ever reach that point of adulthood and Chomper should still be involved, they will be seeing things MY way.
What you guys are saying does seem the most logical, just like it did for the Ahsoka situation till the final episode of season 5, yet there is this little thing called marketability, and it runs against what you're saying.