Shigaraki is not dead in the manga. The storyline has many twists and turns, and his character plays a significant role, so his survival adds to the ongoing drama and suspense.
One common theme is the power dynamic. Fat Gum has a lot of strength and experience, while Fem Kirishima might be portrayed as more of a newbie or someone looking to learn from him. Their relationship can develop around training and growing stronger together.
Well, it's a complex situation. Shigaraki dies as a result of a combination of factors including the coordinated efforts of the heroes and his own overexertion of his abilities.