Question

Do this or you will be punished (convert into complex sentence)

Answer 1

If you will not do this you will be punished

Answer 2

The answer is: Unless you do this, you will be punished.  

Here the sentence is converted into a complex sentence where the principal clause is “you will be punished”.

The subordinate clause is unless you do this.

The original sentence was a compound sentence added with the connector or.

By adding unless, the meaning has got clarified and it reads well.