This kid is an ecological disaster waiting to happen. What happens when he dies, even if from old age, or gets senile or sentimental and just releases all of his slimes back into the wild? He has thousands of them, far more than what their numbers would ordinarily be in a given area, since they are at the bottom of the food chain. As time goes on, they only increase in number. Plus, he has a lot of evolved slimes with powerful abilities. Add in how they are now weapon trained, and are skilled at cooperating with one another in a fight, and you have a recipe for disaster. This wave of slimy destruction could easily wipe out a town, and there are very few in the world (that we have so far seen) who can do more than slow down this plague. As the wave of slime destruction eats people and entire forests, they will only grow in number. There just isn't anywhere that an elderly Ryouma can safely release his slimes that won't cause this annihilation, or would starve out all of his slimes, something that I doubt he would deliberately do. This cataclysm is practically guaranteed to happen because at some point the MC will inevitably die.