Maybe so. Paradox, in their wisdom, seem to think that if the Magyars lose their invasion of Hungary they should still get to keep their 9,000 incredibly OP blokes on horses. This means that if the AI somehow manages to defeat Almos or if Bulgaria is controlled by the player and so actually understands how combat works, they go around raiding anything that borders them that isn't Tengri and there's sod all you can do about that.
FYI, if you defeat raiders in battle, they are forbidden from raiding you for 5 years. This might be a bit more difficult than defeating the invasion (since they won't charge into hills to be slaughtered) but it might still be possible.