Boruto could have visions or dreams that show him Naruto's past. Maybe he enters a forbidden realm or unlocks a secret power that allows him to experience his dad's history.
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.
It's not necessarily a mental illness to want to go back to the past, because this kind of thinking can be a normal human emotional experience. Many people would recall their past experiences and gain inspiration from them. However, if this thought affects daily life and functions, such as social activities, work, or studies, then further evaluation may be needed to determine whether there is any psychological problem.
If you feel that these thoughts have seriously affected your mood, life, or work, it is recommended to seek the help of a professional counselor or doctor for evaluation and treatment. They can provide appropriate advice and support to help overcome this problem.
When Boruto goes back in time, say to the era of the Third Hokage. His relationship with the village elders and the teachers at the ninja academy would be completely new. He would be seen as an oddity since he has knowledge and skills that are not from that time. He might form unexpected friendships with some of the young ninjas of that era. His relationship with his own family members in the past, like his grandparents, would also be very interesting. He could learn a lot about his family's history and values from them, which would change how he views his family in his own time.