Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
There might be. However, it's important to note that this kind of fanfiction is more of a creative and often not part of the official storyline. Some fans really enjoy exploring this kind of relationship between Zoro and Sanji in their own fictional interpretations. They might add interesting plot twists and character developments to make the kiss scenario seem more believable within the world they create in the fanfiction.
Often, they involve a lot of emotional build - up. Since Zoro and Sanji have a complex relationship in the original story, in fanfiction, the kiss might be a result of resolving their differences or a sudden realization of deeper feelings.
I think it might have been a character introduced to add depth to Sanji's backstory and motivations. But without more context, it's hard to say for sure.
As of now, Sanji is very much alive in the One Piece manga. The story keeps unfolding with him as a vital part of the plot. The author hasn't written his death yet.
One popular sanji crossover fanfiction could be where he crosses over with characters from 'One Piece' and other anime like 'Naruto'. In such a story, Sanji might end up in the Hidden Leaf Village and have to cook for Naruto and his friends using his unique cooking skills. His chivalrous behavior would also be an interesting aspect to explore in this new setting.