All I can say is, never say never. (These are just the most recent example I can name, personally.) Surf's Up 2 took a 10 years to come into existence; same for Jurassic World (14 years); The Land Before Time 14 (10 years); Tremors 5 (13 years). Saying Happy Feet 3 won't happen isn't entirely true, considering some series are suddenly given a new installment after 5-10+ years. It's only been around 7 years since Happy Feet 2, so it's bound to get confirmation in the next 3 years at the earliest.