Well, Boruto might have a range of reactions. If the fanfiction shows Naruto as a really powerful and cool hero, which he is, Boruto would probably feel proud. But if it's something that twists Naruto's character in a negative way, he would likely be angry or defensive. He respects his father a great deal, so any false portrayal could upset him. He may also find some of the more out - there or creative fanfictions amusing, like ones that put Naruto in a completely fictional adventure that's way different from what actually happened.
The ending of the Boruto manga is a combination of emotional moments and big reveals. Different characters have their destinies fulfilled in unexpected ways. It's a finale that will leave you thinking, but I suggest you discover it firsthand by reading it.
Boruto would probably be really flustered. He might start stuttering and making excuses, like blaming it on the situation. Sarada, on the other hand, would likely be very shy and might avoid looking at Boruto directly for a while.
No, Boruto is alive in the manga. The plot hasn't led to his death. However, the manga is ongoing, and anything could happen in the later developments.