Ok sorry for the delay. Let me start by explaining how void collapse/nihility collapse/turn null works.
Void collapse gives rimuru the authority over void. He essentially controls void which is nothingness which was used to create the world from nothing.
Now let me explain how diablo regen works. If you resurrect/regen after being erased at a conceptual level and still come back or are said to be able to come back, then you have high-godly regen. Diablo is said to be able to do this when he himself said he is unlike other primordial demons and can come back basically instantly even if he is completely dead. I usually scale him to high godly regen for that reason, there are more but it is too hard to explain that right now so i'll just take that.
Now to actually give scans for how void collapse works.
https://imgur.com/cBWVEXG
https://imgur.com/yzZC5Or
Ok, so i know that is a lot of scans but let me explain. These are all just to show how void works in tensura, and void collapse is just the ability that allows the user to control void. Void is true nothingness, there is nothing before void in tensura. Veldanava himself couldn't control full power of void and lost it. Diablo and testarossa were using it proportional to the level of their ability or the amount they can summon at the moment. Also note that they are using the ability through their connection to rimuru and not directly which if rimuru uses it will probably scale him much much much higher in volume 23.
Ok now back to void, information based regeneration, resurrection based regeneration are completely ineffective thanks to void. No matter the existence value, they will be devoured. I mean this is shown by how diablo was able to fight against feldway, who is so much stronger. There is a lot more thinigs like it is the power to create everything and destroy everything but i'll leave it for now.
Now explaining how it is NEP type 2. It erases completely at information and conceptual level. Nobody can control it at its full power. But strictly based on the shown feats as well it created the world and can destroy the world if uncontrolled. Since it erases down to the fundamental level where nothing works against it (according to the scans essentially), it should qualify for NEP 2.
It is not a character so it is hard to go by vsbw definitions, but the 4 non existence mentioned in vsbw are spiritual, conceptual, information and mental nonexistence. They also mention material, idealistic, and paradoxical. It easily qualifies for materialistic. Idealistic is something possible since "imo" it has specific nondualty which counts for idealistic nonexistence. Paradoxical, i don't even understand how this works so i'll just say no i guess.
So yea, all of these factors including many cannon statements of it being called true/complete nothingness should count for NEP type 2.