The sentence I'd like to say is:
"Yes, it does involve the idea that the face of death brings out the best and the worst in people, yet other themes are involved."
This translates to:
“对，它蕴含着死亡会揭示人们的最好和最坏的方面的含义，但是本故事也有别的内涵。”
Can you use "主题" instead of "内涵"?
No.
主题 = 'main topic'
内涵 = 'meaning/connotation'
In English, the topic of a conversation is often very different from the meaning of the same conversation. The same applies to Chinese.
主题 is a more direct thing, however, 内涵 is more implicit. For example, if a person make a speech, he may try his best to make the audience clear with his 主题 of the speech but for one sentence of his speech, there might be some 内涵 hidden in it which the audience may not understand if they only focus on the literal meaning of the sentence.
