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.
A fanfic could focus on Indra's training. We could write about the intense and arduous training he underwent to become such a powerful figure. It might involve secret techniques passed down in the Otsutsuki clan that only he was able to master due to his unique talent.
Another angle could be a fanfic where Indra Otsutsuki travels to a different dimension. He has to adapt to a completely new world with different rules and powers. It would be fascinating to see how his Otsutsuki abilities fare in this new environment and how he interacts with the local inhabitants.
Yes, there are likely some fanfictions with this concept. Fanfiction writers often come up with unique and creative ideas, and the idea of Naruto having some sort of special connection or relationship with Kaguya Otsutsuki in a fan - created story is not unheard of. It could involve Naruto exploring Kaguya's past, or perhaps having a role in her redemption in the fanfic's alternate universe.
Yes, Boruto is indeed a manga. It expands on the Naruto universe and offers fresh perspectives and storylines. Many fans enjoy reading it to delve deeper into the world created by the series.
Kaguya otsutsuki is often a very popular character. Since she was the progenitor of the otsutsuki in the Naruto canon, fanfictions like to explore more about her backstory and her relationship with other characters. Another popular one is Momoshiki otsutsuki. His powerful abilities and his encounter with Naruto in the series make him a great character to expand on in fanfiction.