AWWWW! Poor Malone! I hope he feels better soon.

If you're doing it for Rilla's happiness, maybe consider getting another cockatiel. She will probably be very happy to have a birdie like her, But I know that she was used to Azure and she might be happy with a parakeet too. If you go to bird websites, they usually don't recommend keeping a tiel and keet in the same cage. They say parakeets, despite their tiny size, sometimes boss tiels around. When I birdiesat my friend's parakeets, her birds kept bossing my birds around and riding their tails. My birds hated that. LOL! If you get a parakeet, I think its best to keep them in different cages next to each other, or make sure they are good with each other if you plan to house them together. Azure got along great with Rilla, but not all birds have the same personality. And when you get your new birdie, be sure to post pics of the new one and Rilla too!