Question: How can we change the following sentence into negative one without changing the meaning? 

> 
> He did everything.
> 
> 
> 

Can we change it into this: 

> 
> He left nothing undone.
> 
> 
> 

Or 

> 
> Didn't he do anything 
> 
> 
>

Answer: 
He did not stop until everything was done.
The question completely misunderstands itself.

'He did everything' is grammatically positive; semantically it means little. Define 'everything', please?

'He left nothing undone' is still positive, unless you think 'he ran away' or 'he surrendered' or 'he lost' grammatically negative. Do you?

'Didn't he do anything?' is a question; not comparable to the other examples.

'He did nothing' is still a positive statement. 'He did (whatever)' will always remain positive.

'He did not do anything' is as close as you could get to a negative statement.