Note though that this is true only for hela=entire, when hela=unbroken it wants "den/det" as usual.
Jag vill ha den hela radion, inte den trasiga. - I want the functioning radio, not the broken one.
Jag vill ha hela pizzan, inte bara en bit. - I want the whole pizza, not just a slice.
It's complicated. In many cases – like here – both work perfectly fine. Just like you can use either will or are going to in English here.
The general idea is that ska is only used for actions that can be controlled or when somebody wants something to happen (or not happen), whereas kommer att can be used in a more neutral way, when you're making some sort of prediction about what is likely to happen. It's a lot more complicated than that, but that's a good place to start.
So if I understand correctly, it's basically the opposite of English, where "going to" indicates intention and "will" indicates prediction? (It's also more complicated in English because "going to" can be used to predict based on immediately perceivable evidence, like seeing a raincloud and saying "It's going to rain.")
Swedish has a lot of overlap as well, and natives will not always agree on which option is the best in any given situation. I'd go as far as claiming that understanding the difference between ska and kommer att can often be one of the very hardest things for any learner.