I think Diablo is the one who will have the least problem of comming back "alive" because he was killed in his own realm (Burning Hells / Chaos Sanctuary). The thing with the soulstones is a bit complicated...when the Horadrim where tasked to imprison the Prime Evils by Tyrael, the soulstones were indeed prisons for them. But Izual told the Prime Evils how to corrupt the stones to be used as a source of power. Mephistos soulstone is destroyed by the player. Diablo soulstone is destroyed in the ending cinematic.
The thing with Baal is more complicated...his soulstone was broken from the beginning(that's why Tal Rasha kept Baal inside himself) and Baal used Tal Rasha as body after the events with Marius in the cinematic. This made him stronger because he had the abilities of the mage Tal Rasha (Baal is actually the weakest of the 3 primes). Baal also gained more power by corrupting the Worldstone. This is why the Worldstone had to be destroyed by tyrael...
Diablo will for sure be there because it is his game...an he is the strongest of the 3 prime evils and killed "at home".
Baal has also nothing much to do in the history of d3 so i don't think we will see him again and beeing the weakest and killed in santuary is also not helping him.
Mephisto could have another role in d3 because he has alot to do with past events in sanctuary etc
I also think that Belial and Asmodan will have some role in the game.
And there has to be some Angels...there are alot that are not happy that sanctuary exists...