"Why do we use Present Simple in the future and when do we do this?" - your corrected question. I wonder if "near future" is one of these pseudo-rules that I hear taught in classrooms. The only real "near future" form we have in English is "be about to (verb)", ie. the action is moments away. The other forms we use for future in English aren't classified by "how soon" they happen. In your examples, "What do you say, love?" basically means "What's your opinion, my dear?" It's asking a simple question. I don't see any future timeframe here. The example, "And what happens?" "He dies" is a narrative form. We can use this in a past timeframe as well. I guess Liza's example of conditionals might be what you want. "He dies" is zero conditional (definite result). "He will die" is first conditional (a very likely result). I guess you've already seen the rules for time-clauses and if-clauses. Like Liza and Su.Ki. have pointed out, Present Simple is used for scheduled events in the future.

Present Simple может кроме собственно настоящего времени означать запланированные события (The concert is next week). Чтобы подчеркнуть, что вы собираетесь что-то сделать, можно использовать Present Continious (We are moving in tomorrow). Кроме того, в условных предложениях может использоваться настоящее время там, где по-русски было бы будущее. - What happens if I hit him with a hammer? - He dies / но я бы скорее сказала he will die. - Что будет, если я ударю его молотком? - Он умрёт. >>What do you say, love? Я бы сказала, что это просторечное использование present simple вместо present continious.

I'm not sure what is meant by 'near future' either. We use the present simple to talk about future time when it's something that's part of a schedule, for example: My train leaves in half an hour. The new school term starts next month. The next Olympics are in 2016.