The MHA manga is way ahead. It's not unusual for manga to progress faster as it doesn't have the production constraints of an anime. So, there's a lot more to discover in the manga that hasn't been animated yet.
Several characters have met their demise in the MHA manga, but it's a bit complex to list them all precisely. Some of the notable ones include [mention specific characters if known].
I think it's hard to say for sure. There are a few characters who could potentially be the traitor, and it's all part of the mystery and suspense of the story.
Right now in the MHA manga, there's a lot of focus on the power struggles and internal conflicts within the hero community. Also, some characters are undergoing significant growth and transformation.