Is Opaline defeated for good and the snow leopard Allaru will be the new main villian?

I wouldn’t count on it. Villains are like Cockroaches.

7908646
I don't think so. She's trapped inside the Unity Tree. I mean until the tree gets damaged or destroyed, she'll be freed

7908647
Or Discord

7908646
She’s trapped inside the new together tree. If the show was that realistic she’d suffocate to death pretty fast, but it’s not that realistic so she’s probably just in a magical hibernation or something. Still the tree would have to be cut down or otherwise damaged enough for her to escape. For now it’s Allura and the rabbit taking over as main baddie.

Unfortunately, this is one of those where we will have to wait and see what will happen, because until then, it's just rumors.