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Of course none of the main characters have died yet, we still have the best part of a decade left with this series. Deaths in One Piece only happen when plot needs it or in flashbacks, I'm perfectly fine with that.
There have certainly been hints at it happening though, he said himself that using gear second techniques will shorten his lifespan. Then there was Emporio's treatment during Impel Down which took a decade off. It also seems as if most of the D characters burn out faster, there are of course exceptions but I'd believe it.
Doubt we'll get any kids from the crew and if we do I doubt it will be internal. The only couple I could actually see happening is Usopp and Kaya.
On the topic of shounen deaths, this Naruto chuunin exam filler added another dead waifu to the mix. First it was Fu and then the
animal summon path of Pain.