Argthtjtr

But it’s these conflicts between life and death that are the works main themes. They echo an important principle in that we shouldn’t fear or challenge death, or the nature of death. That we can meet it half-way by valuing life and respecting and not harming others.

Is the use of 'that/they' here accurate (complete sentences). As the the that and they clauses are referring directly to what's preceded them.

Or do they require conjunctions/semi colon.

These are called sentence fragments. It is common practice to use a dependent clause as a separate sentence when it follows clearly from the preceding main clause in journalistic writing; it is often used for emphasis and style.

Examples in Journalese writing:

The current city policy on housing is incomplete as it stands. Which
is why we believe the proposed amendments should be passed.

Some may disregard you for using such practices in formal or academic situations, personally, I believe it is completely fine to start a sentence with a conjunction:

But it’s these conflicts between life and death that are the works' main themes. They echo an important principle in that we shouldn’t fear or challenge death, or the nature of death. That we can meet it half-way by valuing life and respecting and not harming
others.

The sentence beginning with 'they' is a complete sentence, its antecedent is "these conflicts". So they can be replaced with these conflicts: These conflicts echo an important principle...

However, the that-clause can be seen as a dependent clause preceding from the main clause, "They echo an in important principle...":

They echo an important principle; in that we shouldn't fear or
challenge death, or the nature of death ; that we meet it half-way be
valuing life and respecting and not harming others.

and so it should not be separated. Usually, a dependent clause can be the head of a sentence if it does not precede as a main clause from the previous sentence. However, as you can see if it were not separated it would be an extremely complex sentence. Personally, I would reword it as:

They {these conflicts} echo an important principle: that we shouldn't
fear or challenge death, or the nature of death and that we meet it
half-way by valuing life and respecting and not harming others.

Still, I'd prefer:

They echo an important principle in that we shouldn’t fear or
challenge death, or the nature of death. That we can meet it half-way
by valuing life and respecting and not harming others.

As it is much easier to understand and the emphasis is clear. In terms of rhetoric, the that-clause is syntactically parallel to the but-clause:

But it's these conflicts between life and death that are the works' main themes. // That we can meet it half-way by meet it half-way by valuing life and respecting and not harming others.

How?

1. [Conflicts in life are tiresome], but it's these conflicts between life and death that are the works' main themes.




2. They echo an important principle; in that we shouldn’t fear or challenge death; ... that we can meet it half-way by valuing life and meet it half-way by valuing life and respecting and not harming others.

The things in in (1) is just my interpretation of what could precede the but-clause.

Second sentence subject is a pronoun:"They"

Pronoun refers to the "conflicts between life and death" from the previous sentence.

Verb is "echo".

Main sentence structure is "They echo".

This is correct.

Direct object of the sentence is "principle".

Extended sentence structure is [subject] [verb] [direct object].

We now have

"They echo (a) principle".

Prepositional phrase that modifies the direct object ("principle") by describing it more specifically is "in that we shouldn’t fear or challenge death, or the nature of death."

This is complicated and difficult to read, because it is attached to the direct object, because it is a phrase, the phrase is about an abstract subject we don't deal with in our daily lives, and because that phrase also contains TWO(!) conjunctive "or" words! You reader's mind has to work hard to determine the "or"'s are conjunctions and NOT conditional clauses.

This awful. It tortures the reader with complexity. It is technically correct use of the language, but it demands your readers perform mental gymnastics to understand it.

Subject of the next sentence is a prepositional phrase: "That we can meet"
AND THE VERB IS ABSENT.

This sentence is therefore broken. What went wrong?

I suspect you wanted to include TWO prepositional phrases in the previous sentence, which is abominable, because the previous sentence is already too complex.

Even if we steal the intended root sentence structure from the previous sentence, we again get: [subject][verb][direct object][prepositional phrase modifying direct object]

They echo principle [that we can meet IT halfway]

Here the "IT" refers to the word "death" from TWO SENTENCES AGO. This is an abusive way to treat your readership. Normal humans can't trace the maze of meaning backward in time to the word "death" because you already overflowed the capacity of their short-term memory with a complicated prepositional phrase containing TWO conjunctive "or"'s.

The last sentence is then screwed-up by including TWO conjunctive "and"'s, without the needed comma after "valuing life".

Please, please, please simplify your writing. Make complete, separate sentences out of each phrase. Don't separate your pronouns from the subject they refer to. Restate the subject instead.

Also, the very first sentence needs to include a possessive apostrophe in "work's".