Sure, Doctor Strange has been part of the Avengers in the comic universe. His magical expertise added a unique dimension to the team's capabilities and strategies.
I wouldn't say Doctor Strange comics are niche. They offer unique storylines and magical elements that attract a specific group of fans. But they haven't achieved the same level of mass popularity as the most well-known comic franchises.
Doctor Strange's fate in the comics can be quite complex. Sometimes he seems to die but returns through various plot devices or magical means. It really depends on the specific comic arc and creative direction.