Learn Italian: Il superstite non è rimasto ferito, ma è illeso. - The survivor did not remain injured, but he is unharmed.

Using rimanere (or restare) as the auxiliary instead of essere emphasizes the final state or result of an event. While è stato ferito focuses on the action of being injured by something or someone, è rimasto ferito focuses on his condition after the event, much like saying he "ended up injured" or "was left injured."

The given meaning says "did not remain injured." Does rimanere ferito always mean someone "remained" injured?

Not exactly. While the literal translation is "remained injured," Italian uses rimanere ferito as the standard way to say someone "got injured" or "was injured" in an accident. It means the event left them in that state, not that they were already injured and stayed that way. A more natural English equivalent would simply be "The survivor wasn't injured."

Is superstite a masculine or feminine noun?

It can be both! Superstite (survivor) is a noun that ends in -e, and its ending doesn't change based on gender. You determine the gender by looking at the article. Here, il superstite tells us the survivor is male. If it were a female survivor, it would be la superstite.

Are ferito and illeso both past participles here?